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I was wondering why semi-trucks are called that. Doesn’t semi mean “part of”? A semi-truck is a whole truck if I ever saw one!

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Semi truck or semi is short for semi-trailer truck.¹ The prefix semi- literally means half.² The term describes a truck consisting of a tractor and a semi-trailer. A semi-trailer is semi-supported (half supported) by its own wheels, which support only the rear of the trailer. The front of the trailer is supported by the rear wheels of the tractor.³

picture of a semi-trailer truck

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  • Yes, see this link for more explanation. – Jim Aug 2 '12 at 0:12
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    AKA "tractor trailer" – Bob Aug 2 '12 at 1:14
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    In Australia we call the pictured contraption (including the truck body) a "semi-trailer", and the truck/tractor bit when referred to separately a "prime mover". – John Lyon Aug 2 '12 at 6:39
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    And in the UK this is called an "articulated lorry", or sometimes just an "artic". – Martin Aug 2 '12 at 7:44
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    @Martin: or Juggernaut! – e100 Aug 2 '12 at 10:32

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