Definition of "frenulum"

(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.  examples

(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.