The word 'tailgate' is a transparent compound formed from two native English elements. 'Tail' originates from the Old English 'tægl', referring to the rear appendage of an animal, a concept extended metaphorically to denote the hindmost part of any object. 'Gate' derives from Old English 'gæt' or 'geat', meaning an opening or door. The literal combination, first used in the late 19th century, perfectly describes the rear, door-like panel of a wagon or truck. The verb sense, meaning to drive dangerously close behind another vehicle, emerged in the mid-20th century by metaphorically visualizing the following car as if it were attached to the 'tail' of the lead vehicle. The social event meaning, originating in American English around the 1960s, derives from the practice of gathering around the open tailgate of a station wagon or pickup truck in a parking lot.

Structure: tail + gate tail (Old English: tægl, meaning the hindmost part of an animal or object; functional role: root, indicating position or rear part) gate (Old English: gæt, geat, meaning an opening, door, or passage; functional role: root, indicating a barrier or opening)