labium

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Anatomy Any of four folds of tissue of the female external genitalia.
2. n. Zoology A liplike structure, such as that forming the floor of the mouth of certain invertebrates, especially insects.
3. n. Zoology The inner margin of the opening of a gastropod shell.
4. n. Botany One of the liplike divisions of a labiate corolla.

Century Dictionary and Cyclopedia

1. n. In anatomy and zoology, a lip or lip-like part. Specifically. In anatomy:
2. n. In bot:
3. n. The lower or anterior lip of a bilabiate corolla
4. n. In Isoëtes, a lip-like structure formed by the lower margin of the foveola.
5. n. [capitalized] A genus of ichneumon-flies, with one small New Guinean species

Wiktionary

1. n. anatomy A liplike structure; especially one of the two pairs of folds of skin either side of the vulva.
2. n. botany The lip of a labiate corolla.
3. n. music The lip against which pressured air is driven in a flue pipe in an organ.

GNU Webster's 1913

1. n. A lip, or liplike organ.
2. n. The lip of an organ pipe.
3. n. (Anat.) The folds of integument at the opening of the vulva.
4. n. The organ of insects which covers the mouth beneath, and serves as an under lip. It consists of the second pair of maxillæ, 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).
5. n. Inner margin of the aperture of a shell.

WordNet 3.0

1. n. a liplike structure that bounds a bodily orifice (especially any of the four labiate folds of a woman's vulva)