Source : Webster's Revised Unabridged Dictionary (1913)

Trillium \Tril"li*um\, n. [NL.; cf. L. trilix triple-woven,
   triple.] (Bot.)
   A genus of liliaceous plants; the three-leaved nightshade; --
   so called because all the parts of the plant are in threes.

Source : WordNet®

trillium
     n : any liliaceous plant of the genus Trillium having a whorl of
         three leaves at the top of the stem with a single
         three-petaled flower [syn: {wood lily}, {wake-robin}]