Source : Webster's Revised Unabridged Dictionary (1913)

Gnathidium \Gna*thid"i*um\, n.; pl. {Gnathidia}. [NL., fr. Gr. ?
   the jaw.] (Zo["o]l.)
   The ramus of the lower jaw of a bird as far as it is naked;
   -- commonly used in the plural.