TRILLIUM

trillium, wood lily, wake-robin

(noun) 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

Source: WordNet® 3.1

Etymology

From the genus name.

Noun

trillium (plural trilliums)

Any of several perennial flowering plants, of the genus Trillium, having flowers with three petals

Source: Wiktionary

Tril"li*um, n. Etym: [NL.; cf. L. trilix triple-woven, triple.] (Bot.)

Definition: A genus of liliaceous plants; the three-leaved nightshade; -- so called because all the parts of the plant are in threes.

Source: Webster’s Unabridged Dictionary 1913 Edition