semi-tractor

The engine, operator's cabin, and hitch, together called the tractor, of a "semi-tractor trailer", comprising the forward part, which tows a trailer hitched thereto; {{US}} a "semi" , a trailer truck, a tractor trailer, an eighteen wheeler. Sometimes two {{US|and|Australia}} and as many as three {{Australia}} trailers may be towed. The trailer often is enclosed, refrigerated, etc.