The Collaborative International Dictionary of English v.0.48:

Gnathonic \Gna*thon"ic\, Gnathonical \Gna*thon"ic*al\, a. [L.
   Gnatho, name of a parasite in the "Eunuchus" of Terence, Gr.
   ?; hence, a parasite in general.]
   Flattering; deceitful. [Obs.]
   [1913 Webster]