noun
- an airplane with one main sustaining surface or one set of wings.
- Nautical. a planing craft the bottom of which is in an unbroken fore-and-aft line.
noun
- an aeroplane with only one pair of wingsCompare biplane
n.1907, a hybrid coined from mono- + second element of aeroplane. In old planes the wings formed a single surface running across the fuselage.