A truck that has a cab but no body; used for pulling large trailers or vans WordNet 3.0 & Open English WordNet

A tractor unit, also known as a truck unit, lorry unit, power unit, prime mover, ten-wheeler, semi-tractor, semi-truck, semi-lorry, tractor cab, truck cab, lorry cab, big rig tractor, big rig truck or big rig lorry or simply a tractor, truck, lorry, semi, big rig or rig, is a characteristically heavy-duty towing engine that provides motive power for hauling a towed or trailered load. Wikipedia

Characteristically heavy-duty towing engine that provides motive power for hauling a towed or trailered load Wikidata

A large road vehicle, usually consisting of a two or three-axled chassis, and fitted with a cab, engine and drivetrain, used for hauling semitrailers. Wiktionary

Road vehicle. Wiktionary (translation)