Merriam-Webster Collegiate Dictionary - frenulum

 noun  (plural frenula)  Etymology: New Latin, diminutive of Latin frenum  Date: circa 1706  1. a connecting fold of membrane serving to support or restrain a part (as the tongue)  2. a bristle or group of bristles on the front edge of the posterior wings of some lepidoptera that unites the wings by interlocking with a catch on the posterior part of the forewings