The Collaborative International Dictionary of English v.0.48:

Euphorbia \Eu*phor"bi*a\, n. [NL., fr. L. euphorbea. See
   Euphorrium.] (Bot.)
   Spurge, or bastard spurge, a genus of plants of many species,
   mostly shrubby, herbaceous succulents, affording an acrid,
   milky juice. Some of them are armed with thorns. Most of them
   yield powerful emetic and cathartic products. Euphorbiaceous

WordNet (r) 3.0 (2006):

Euphorbia
    n 1: type genus of the Euphorbiaceae: very large genus of
         diverse plants all having milky juice [syn: Euphorbia,
         genus Euphorbia]