Source : Webster's Revised Unabridged Dictionary (1913)

Osmaterium \Os`ma*te"ri*um\, n.; pl. {Osmateria}. [NL., fr. Gr.
   ? smell.] (Zo["o]l.)
   One of a pair of scent organs which the larv[ae] of certain
   butterflies emit from the first body segment, either above or
   below.