The compound 'tractor-trailer' is a modern, descriptive term from the 20th-century transportation industry. Its first element, 'tractor', originates from the Latin verb trahere ('to pull, draw'), which evolved into a machine name for a vehicle that pulls heavy loads. The second element, 'trailer', derives from the English verb 'to trail', meaning to follow or be drawn behind, itself from a Germanic root related to dragging. The compound's logic is perfectly literal: it names the complete vehicle by specifying its two core, functional components—the pulling unit (tractor) and the cargo unit being pulled (trailer). This transparent construction efficiently describes the articulated nature of the road vehicle.

Structure: tractor (pulling vehicle) + trailer (vehicle pulled) - tractor: From Latin tractus (past participle of trahere, meaning 'to pull, draw'). In English, it functions as an agent noun meaning 'that which pulls'. - trailer: From the verb trail (meaning 'to pull or draw along behind'), of Germanic origin, with the agent suffix -er. It denotes a vehicle designed to be pulled.