Source : Webster's Revised Unabridged Dictionary (1913)

Fraenum \Fr[ae]"num\, or Frenum \Fre"num\, n.; pl. E.
   {Fr[ae]nums}, L. {Fr[ae]na}. [L., a bridle.] (Anat.)
   A connecting fold of membrane serving to support or restrain
   any part; as, the fr[ae]num of the tongue.