The Collaborative International Dictionary of English v.0.48:

Coreopsis \Co`re*op"sis\ (k[=o]`r[-e]*[o^]p"s[i^]s), prop. n.
   [NL., fr. Gr. ko`ris bug + 'o`psis appearance.] (Bot.)
   A genus of herbaceous composite plants, having the achenes
   two-horned and remotely resembling some insect; tickseed.
   Coreopsis tinctoria, of the Western plains, the commonest
   plant of the genus, has been used in dyeing.
   [1913 Webster]

WordNet (r) 3.0 (2006):

coreopsis
    n 1: any of numerous plants of the genus Coreopsis having a
         profusion of showy usually yellow daisylike flowers over
         long periods; North and South America [syn: coreopsis,
         tickseed, tickweed, tick-weed]