Merriam-Webster Collegiate Dictionary - labium

 noun  (plural labia)  Etymology: New Latin, from Latin, lip — more at lip  Date: 1634  1. any of the folds at the margin of the vulva — compare labia majora, labia minora  2. the lower lip of a labiate corolla  3.  a. a lower mouthpart of an insect that is formed by the second pair of maxillae united in the middle line  b. a liplike part of various invertebrates