The Collaborative International Dictionary of English v.0.48:

Poinsettia \Poin*set"ti*a\ (poin*s[e^]t"t[i^]*[.a]), n. [NL.
   Named after Joel R. Poinsett of South Carolina.] (Bot.)
   A Mexican shrub (Euphorbia pulcherrima) with very large and
   conspicuous vermilion bracts below the yellowish flowers.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Euphorbia pulcherrima
    n 1: tropical American plant having poisonous milk and showy
         tapering usually scarlet petallike leaves surrounding small
         yellow flowers [syn: poinsettia, Christmas star,
         Christmas flower, lobster plant, Mexican flameleaf,
         painted leaf, Euphorbia pulcherrima]