labium

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Anatomy Any of four folds of tissue of the female external genitals.
• noun A liplike structure, such as that forming the floor of the mouth of certain invertebrates, especially insects.
• noun The inner margin of the opening of a gastropod shell.
• noun Botany One of the liplike divisions of a bilabiate corolla.

from The Century Dictionary.

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

from the GNU version of the Collaborative International Dictionary of English.

• noun A lip, or liplike organ.
• noun The lip of an organ pipe.
• noun (Anat.) The folds of integument at the opening of the vulva.
• noun 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).
• noun Inner margin of the aperture of a shell.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

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

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

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