semi-trailer

noun

1. Also called semi. a detachable trailer for hauling freight, with wheels at the rear end, the forward end being supported by the rear of a truck tractor when attached.Compare full trailer.
2. tractor-trailer.

noun

1. a type of trailer or articulated lorry that has wheels only at the rear, the front end being supported by the towing vehicle

n.also semitrailer, 1910 in reference to motor vehicles (late 19c. in botany), from semi- + trailer.Short form semi is attested from 1942.