frenulum

Etymology

Borrowed from New Latin frēnulum, diminutive of frēnum (“a bridle, curb, bit”).

noun

1. (anatomy) A small fold or ridge of tissue that supports or restrains the motion of the part to which it is attached, in particular a fold of skin beneath the tongue, or between the lip and the gum.
   Humans have three oral frenulums: beneath the tongue, between the upper lip and gum, and between the lower lip and gum.
2. (entomology, zootomy) A bristle or row of bristles on the edge of the hindwings of some lepidoptera which unites the wings by interlocking with a catch on the posterior part of the forewings.