The Collaborative International Dictionary of English v.0.48:

Clematis \Clem"a*tis\ (kl[e^]m"[.a]*t[i^]s), n. [NL., fr. Gr.
   klhmati`s brushwood, also (from its long, lithe branches)
   clematis. fr. klh^ma twig, shoot, fr. kla^n to break off.]
   (Bot.)
   A genus of flowering plants, of many species, mostly
   climbers, having feathery styles, which greatly enlarge in
   the fruit; -- called also virgin's bower.
   [1913 Webster]

WordNet (r) 3.0 (2006):

clematis
    n 1: any of various ornamental climbing plants of the genus
         Clematis usually having showy flowers