[1] : The Collaborative International Dictionary of English v.0.48

trionyx \trion"yx\, n. nl., fr. gr. ? see tri- + ? a
   claw. zool.
   a genus of fresh-water or river turtles which have the shell
   imperfectly developed and covered with a soft leathery skin.
   they are noted for their agility and rapacity. called also
   soft tortoise, soft-shell tortoise, and mud turtle.
   1913 webster

   note: the common american species trionyx ferox syn.
         aspidonectus ferox becomes over a foot in length and
         is very voracious. similar species are found in asia
         and africa.
         1913 webster
see also:
tri- soft tortoise soft-shell tortoise mud turtle trionyx ferox aspidonectus ferox 

[2] : WordNet (r) 2.0

trionyx
     n : type genus of the trionychidae syn: genus trionyx
see also:
genus trionyx 

Trionyx >> T Words
Trionyx, definition of term: Trionyx
trionyx_pag1.html