# Is there a name for this polygon? **URL:** \ **Category:** Factual Questions\ **Created:** [August 30, 2025, 4:34pm UTC](https://boards.straightdope.com/t/is-there-a-name-for-this-polygon/1022604 "2025-08-30T16:34:31Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Little\_Nemo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/little_nemo/32/3120_2.png) [@Little\_Nemo](https://boards.straightdope.com/u/Little_Nemo)\ **Post date:** [August 30, 2025, 4:34pm UTC](https://boards.straightdope.com/t/is-there-a-name-for-this-polygon/1022604/1 "2025-08-30T16:34:31Z")
Picture a circle. Put a point inside it. Draw two lines from the point at an acute angle out to the circle’s perimeter. You have a shape that’s similar to a triangle but with two straight lines and one curved line. Basically the same shape as a slice of pizza. Is there a name for this polygon? ---
**Author:** ![Prof.Pepperwinkle](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/prof.pepperwinkle/32/13627_2.png) [@Prof.Pepperwinkle](https://boards.straightdope.com/u/Prof.Pepperwinkle)\ **Post date:** [August 30, 2025, 4:39pm UTC](https://boards.straightdope.com/t/is-there-a-name-for-this-polygon/1022604/2 "2025-08-30T16:39:02Z")
[A **triangle with a curved side** is commonly referred to as a **Reuleaux triangle**.](https://www.bing.com/ck/a?!&&p=7140b2c3360789ef484c8b7e7901185d98329ac18d6c0149c2aa32b83b4b5140JmltdHM9MTc1NjUxMjAwMA&ptn=3&ver=2&hsh=4&fclid=0f33764d-0369-6040-35cf-663502c16139&u=a1aHR0cHM6Ly9lbi53aWtpcGVkaWEub3JnL3dpa2kvUmV1bGVhdXhfdHJpYW5nbGU&ntb=1) The IPA pronunciation is [ʁœlo]. Approximately, hrur-lo. ---
**Author:** ![Little\_Nemo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/little_nemo/32/3120_2.png) [@Little\_Nemo](https://boards.straightdope.com/u/Little_Nemo)\ **Post date:** [August 30, 2025, 4:41pm UTC](https://boards.straightdope.com/t/is-there-a-name-for-this-polygon/1022604/3 "2025-08-30T16:41:15Z")
If I’m understanding the concept correctly, a Reuleaux triangle has three curved sides. I’m thinking about a polygon with two straight sides and one curved side. ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [August 30, 2025, 5:07pm UTC](https://boards.straightdope.com/t/is-there-a-name-for-this-polygon/1022604/4 "2025-08-30T17:07:40Z")
If the point is at the center of the circle, it’s a sector. I’m not sure if there’s a more general term for any triangle with an arc for one side. ---
**Author:** ![Beckdawrek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beckdawrek/32/3647_2.png) [@Beckdawrek](https://boards.straightdope.com/u/Beckdawrek)\ **Post date:** [August 30, 2025, 5:08pm UTC](https://boards.straightdope.com/t/is-there-a-name-for-this-polygon/1022604/5 "2025-08-30T17:08:57Z")
Yes. Sector of a circle. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 30, 2025, 5:09pm UTC](https://boards.straightdope.com/t/is-there-a-name-for-this-polygon/1022604/6 "2025-08-30T17:09:18Z")
Just to nitpick, this shape wouldn’t be a polygon, because all of a polygon’s edges are straight line segments. But yeah, what @Lumpy said: If the point is at the center, it’s a sector, otherwise I don’t think there’s a name. ---
**Author:** ![mixdenny](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mixdenny/32/2962_2.png) [@mixdenny](https://boards.straightdope.com/u/mixdenny)\ **Post date:** [August 30, 2025, 5:09pm UTC](https://boards.straightdope.com/t/is-there-a-name-for-this-polygon/1022604/7 "2025-08-30T17:09:19Z")
A sector. ---
**Author:** ![xtenkfarpl](https://avatars.discourse-cdn.com/v4/letter/x/c2a13f/32.png) [@xtenkfarpl](https://boards.straightdope.com/u/xtenkfarpl)\ **Post date:** [August 30, 2025, 5:21pm UTC](https://boards.straightdope.com/t/is-there-a-name-for-this-polygon/1022604/8 "2025-08-30T17:21:40Z")
Though if there weren’t already a name, pizzagon would be appropriate…? ---
**Author:** ![Little\_Nemo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/little_nemo/32/3120_2.png) [@Little\_Nemo](https://boards.straightdope.com/u/Little_Nemo)\ **Post date:** [August 30, 2025, 5:24pm UTC](https://boards.straightdope.com/t/is-there-a-name-for-this-polygon/1022604/9 "2025-08-30T17:24:14Z")
> [@Chronos](#): > > Just to nitpick, this shape wouldn’t be a polygon, because all of a polygon’s edges are straight line segments. Okay, what’s the name for a region of a plane that’s bound by enclosed curves? I know a disk is the technical term for a region that’s bound by a circle. But what’s the more general term? ---
**Author:** ![Little\_Nemo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/little_nemo/32/3120_2.png) [@Little\_Nemo](https://boards.straightdope.com/u/Little_Nemo)\ **Post date:** [August 30, 2025, 5:27pm UTC](https://boards.straightdope.com/t/is-there-a-name-for-this-polygon/1022604/10 "2025-08-30T17:27:36Z")
A sector would be one example of the shape I’m describing. But it would also be possible to have similar shapes that aren’t sectors because the point where the two straight lines meet wouldn’t be the center of the curve described by the curved line. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 30, 2025, 5:37pm UTC](https://boards.straightdope.com/t/is-there-a-name-for-this-polygon/1022604/11 "2025-08-30T17:37:23Z")
> [@Little\_Nemo](#): > > Okay, what’s the name for a region of a plane that’s bound by enclosed curves? If there are no straight edges, then it’s a “curvilinear shape”. With a mixture of straight and curved edges, I don’t think there’s any term more specific than “shape”. But hey, you can take that as an opportunity. If nobody else has come up with a term for something, you can do so yourself. ---
**Author:** ![Zoobi](https://avatars.discourse-cdn.com/v4/letter/z/13edae/32.png) [@Zoobi](https://boards.straightdope.com/u/Zoobi)\ **Post date:** [August 30, 2025, 6:04pm UTC](https://boards.straightdope.com/t/is-there-a-name-for-this-polygon/1022604/12 "2025-08-30T18:04:07Z")
Lamina might be close to an umbrella term for a planar closed curve. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [August 30, 2025, 6:07pm UTC](https://boards.straightdope.com/t/is-there-a-name-for-this-polygon/1022604/13 "2025-08-30T18:07:13Z")
Wouldn’t “wedge” work wonderfully? ---
**Author:** ![Little\_Nemo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/little_nemo/32/3120_2.png) [@Little\_Nemo](https://boards.straightdope.com/u/Little_Nemo)\ **Post date:** [August 30, 2025, 7:58pm UTC](https://boards.straightdope.com/t/is-there-a-name-for-this-polygon/1022604/14 "2025-08-30T19:58:04Z")
The issue arose because of an online puzzle I saw. [![](https://scontent-ord5-3.xx.fbcdn.net/v/t39.30808-6/495135864_1094532919369793_532389819564826044_n.jpg?stp=dst-jpg_s640x640_tt6&_nc_cat=107&ccb=1-7&_nc_sid=127cfc&_nc_ohc=xZcfe8KFnNkQ7kNvwF3Hijl&_nc_oc=AdmZdVgtadLn1nKwudMeov4yO3whyG3jRwY6W4CaFtcaqKytXDhwC05hxtrinOWuP_ncGkXXrORyh35qMwIH1L6E&_nc_zt=23&_nc_ht=scontent-ord5-3.xx&_nc_gid=GDKjoS3jDu3yVvKprSosrw&oh=00_AfVBg6uhkaMHMV8eD4WgxfRBUCDy4Vl4fzNvvg0KcEeqeQ&oe=68B932F7) ](https://scontent-ord5-3.xx.fbcdn.net/v/t39.30808-6/495135864_1094532919369793_532389819564826044_n.jpg?stp=dst-jpg_s640x640_tt6&_nc_cat=107&ccb=1-7&_nc_sid=127cfc&_nc_ohc=xZcfe8KFnNkQ7kNvwF3Hijl&_nc_oc=AdmZdVgtadLn1nKwudMeov4yO3whyG3jRwY6W4CaFtcaqKytXDhwC05hxtrinOWuP_ncGkXXrORyh35qMwIH1L6E&_nc_zt=23&_nc_ht=scontent-ord5-3.xx&_nc_gid=GDKjoS3jDu3yVvKprSosrw&oh=00_AfVBg6uhkaMHMV8eD4WgxfRBUCDy4Vl4fzNvvg0KcEeqeQ&oe=68B932F7) The comments got into arguments where some people were saying the correct answer was three (which is right) but a number of other people were answering with higher numbers because they felt you can have a triangle with a curved side. So I was wondering if there was a technical term for this shape so we could say something like “Those aren’t triangles. They’re pizzagons. Pizzagons aren’t triangles.” ---
**Author:** ![Little\_Nemo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/little_nemo/32/3120_2.png) [@Little\_Nemo](https://boards.straightdope.com/u/Little_Nemo)\ **Post date:** [August 30, 2025, 8:01pm UTC](https://boards.straightdope.com/t/is-there-a-name-for-this-polygon/1022604/15 "2025-08-30T20:01:05Z")
> [@Chronos](#): > > If there are no straight edges, then it’s a “curvilinear shape”. > > With a mixture of straight and curved edges, I don’t think there’s any term more specific than “shape”. You would think we would have made advances in the field in the 2300 years since Euclid. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [August 30, 2025, 8:21pm UTC](https://boards.straightdope.com/t/is-there-a-name-for-this-polygon/1022604/16 "2025-08-30T20:21:37Z")
Not a very technical term but I’d call it a pie slice - a _regular_ pie slice being a sector. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 30, 2025, 8:32pm UTC](https://boards.straightdope.com/t/is-there-a-name-for-this-polygon/1022604/17 "2025-08-30T20:32:55Z")
> [@Little\_Nemo](#): > > You would think we would have made advances in the field in the 2300 years since Euclid. We have, plenty of them. But coming up with new names for things isn’t much of an advance. ---
**Author:** ![Little\_Nemo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/little_nemo/32/3120_2.png) [@Little\_Nemo](https://boards.straightdope.com/u/Little_Nemo)\ **Post date:** [August 30, 2025, 9:12pm UTC](https://boards.straightdope.com/t/is-there-a-name-for-this-polygon/1022604/18 "2025-08-30T21:12:35Z")
Still, you’d think “an area of a plane that’s separated from the rest of the plane by an enclosed line” would be a very basic term in geometry. Calling it a shape seems so imprecise. ---
**Author:** ![RTFirefly](https://avatars.discourse-cdn.com/v4/letter/r/c77e96/32.png) [@RTFirefly](https://boards.straightdope.com/u/RTFirefly)\ **Post date:** [August 30, 2025, 9:46pm UTC](https://boards.straightdope.com/t/is-there-a-name-for-this-polygon/1022604/19 "2025-08-30T21:46:16Z")
> [@Little\_Nemo](#): > > They’re pizzagons. Ordered pizza for three hungry teenagers. It arrived an hour ago. Pizzagon. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [August 30, 2025, 10:19pm UTC](https://boards.straightdope.com/t/is-there-a-name-for-this-polygon/1022604/20 "2025-08-30T22:19:23Z")
Pi slice? [Next page](https://boards.straightdope.com/t/is-there-a-name-for-this-polygon/1022604.md?page=2)