1. A lip, or liplike organ.
2. The lip of an organ pipe.
3. (Science: anatomy) The folds of integument at the opening of the vulva.
4. (Science: zoology) The organ of insects which covers the mouth beneath, and serves as an under lip. It consists of the second pair of maxillae, usually closely united in the middle line, but bearing a pair of palpi in most insects. It often consists of a thin anterior part (ligula or palpiger) and a firmer posterior plate (mentum). Inner margin of the aperture of a shell.