noun a lip, or liplike organ.
2. labium ·noun the lip of an organ pipe.
3. labium ·noun inner margin of the aperture of a shell.
4. labium ·noun the folds of integument at the opening of the vulva.
5. labium ·noun 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).