# truck = semi ?

**URL:** <https://boards.straightdope.com/t/truck-semi/79653>\
**Category:** Factual Questions\
**Created:** [September 4, 2001, 1:05pm UTC](https://boards.straightdope.com/t/truck-semi/79653 "2001-09-04T13:05:05Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Spyderman](https://avatars.discourse-cdn.com/v4/letter/s/e79b87/32.png) [@Spyderman](https://boards.straightdope.com/u/Spyderman)\
**Post date:** [September 4, 2001, 1:05pm UTC](https://boards.straightdope.com/t/truck-semi/79653/1 "2001-09-04T13:05:05Z")

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Why are tractor trailers’ (trucks) referred to as semi’s? Exactly what are they half of?

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**Author:** ![Damhna](https://avatars.discourse-cdn.com/v4/letter/d/3bc359/32.png) [@Damhna](https://boards.straightdope.com/u/Damhna)\
**Post date:** [September 4, 2001, 1:09pm UTC](https://boards.straightdope.com/t/truck-semi/79653/2 "2001-09-04T13:09:04Z")

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They are semi-articulated.

They can’t really talk proper you see 🙂

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**Author:** ![Jet\_Jaguar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jet_jaguar/32/3562_2.png) [@Jet\_Jaguar](https://boards.straightdope.com/u/Jet_Jaguar)\
**Post date:** [September 4, 2001, 1:11pm UTC](https://boards.straightdope.com/t/truck-semi/79653/3 "2001-09-04T13:11:17Z")

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They’re half of a trailer. A semi-trailer only has wheels near the back, and part of it’s weight is resting on the back of the tractor.

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**Author:** ![DVous\_Means](https://avatars.discourse-cdn.com/v4/letter/d/9fc29f/32.png) [@DVous\_Means](https://boards.straightdope.com/u/DVous_Means)\
**Post date:** [September 4, 2001, 1:52pm UTC](https://boards.straightdope.com/t/truck-semi/79653/4 "2001-09-04T13:52:34Z")

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In Australia, our interpretation of the term “semitrailer” is that of the complete unit: truck plus trailer. We refer to the truck on its own as the prime-mover. I think Americans refer to it as a tractor.

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**Author:** ![C\_K\_Dexter\_Haven](https://avatars.discourse-cdn.com/v4/letter/c/b2d939/32.png) [@C\_K\_Dexter\_Haven](https://boards.straightdope.com/u/C_K_Dexter_Haven)\
**Post date:** [September 4, 2001, 2:13pm UTC](https://boards.straightdope.com/t/truck-semi/79653/5 "2001-09-04T14:13:36Z")

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Sigh. [Why are tractor-trailer rigs called “semis”?](http://www.straightdope.com/mailbag/msemi.html)