The Collaborative International Dictionary of English v.0.48:

Plectognath \Plec"tog*nath\, a. (Zool.)
   Of or pertaining to the Plectognathi. -- n. One of the
   Plectognathi.
   [1913 Webster]

WordNet (r) 3.0 (2006):

plectognath
    n 1: tropical marine fishes having the teeth fused into a beak
         and thick skin covered with bony plates or spines [syn:
         plectognath, plectognath fish]