The Collaborative International Dictionary of English v.0.48:

Tetrodont \Tet"ro*dont\, a. (Zool.)
   Of or pertaining to the tetrodons. -- n. A tetrodon. [Written
   also tetradont, and tetraodont.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Tetradont \Tet"ra*dont\, a. & n. (Zool.)
   See Tetrodont.
   [1913 Webster] Tetradrachm