# Why are 18-wheelers called "semi's"?

**URL:** <https://boards.straightdope.com/t/why-are-18-wheelers-called-semis/459630>\
**Category:** Factual Questions\
**Created:** [August 11, 2008, 5:40pm UTC](https://boards.straightdope.com/t/why-are-18-wheelers-called-semis/459630 "2008-08-11T17:40:15Z")\
**Posts on this page:** 3\
**Page:** 3

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**Author:** ![TheLoadedDog](https://avatars.discourse-cdn.com/v4/letter/t/35a633/32.png) [@TheLoadedDog](https://boards.straightdope.com/u/TheLoadedDog)\
**Post date:** [August 12, 2008, 8:16am UTC](https://boards.straightdope.com/t/why-are-18-wheelers-called-semis/459630/41 "2008-08-12T08:16:59Z")

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[QUOTE=Krokodil]  
What is the greatest number of trailers a tractor will pull? Out west, I see as many as three, but around here, just one.  
[/QUOTE]

[112](http://www.abc.net.au/rural/news/content/2006/s1573956.htm)

On a typical road train, I think it’s more like three or four.

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**Author:** ![Tim\_T-Bonham.net](https://avatars.discourse-cdn.com/v4/letter/t/46a35a/32.png) [@Tim\_T-Bonham.net](https://boards.straightdope.com/u/Tim_T-Bonham.net)\
**Post date:** [August 12, 2008, 8:54am UTC](https://boards.straightdope.com/t/why-are-18-wheelers-called-semis/459630/42 "2008-08-12T08:54:47Z")

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[QUOTE=CookingWithGas]  
American English hates a long phrase if a short phrase works just as well.  
[/QUOTE]  
And so does just about every other language.

Long words are less frequently used than short words, in natural languages. Longer words or multi-word phrases, as they begin to be used more frequently, become shorter.

Thus _television receiver set_ becomes _television_ becomes _TV_.

In the science of linguistics, this is known as _Zipf’s Law_.

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**Author:** ![Spoons](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/spoons/32/3141_2.png) [@Spoons](https://boards.straightdope.com/u/Spoons)\
**Post date:** [August 12, 2008, 2:25pm UTC](https://boards.straightdope.com/t/why-are-18-wheelers-called-semis/459630/43 "2008-08-12T14:25:34Z")

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[QUOTE=dbuzman]  
No, Cab-over Pete had a reefer on (was pulling a refrigerated trailer).  
[/QUOTE]  
Remember that the truck names in the song referred to the trucks themselves–“Cab-over Pete” was a cab-over Peterbilt. The song also mentions “a Jimmy hauling hogs,” which would be a GMC truck.

As for fuel capacity, I seem to recall that 900 liters (about 238 gallons) was a typical full tank back when I did some driving. At least it was on the trucks I drove (I didn’t drive reefers).

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