quad bike

From quad (“four (“4”)”) +‎ bike (“bicycle”). From being a 4-wheeled quadricycle vehicle that is ridden astride like a dirt bike (“motorcycle”). The oxymoronic character of the term, via the etymonic-level contradiction of quad ("four") in juxtaposition with the bi- behind bike ("two"), is simply ignored by idiom, as such contradictions often are.

quad bike (plural quad bikes)

2. A small off-road four-wheeled powered vehicle, especially of a design derived from a motorcycle, usually used for recreation or farm work.

   Synonyms: quad, four-wheeler

   Hypernyms: ATV, all-terrain vehicle < vehicle

   Coordinate terms: three-wheeler; dirtbike; UTV, SxS, side-by-side