The Collaborative International Dictionary of English v.0.48:

Cleavers \Cleav"ers\, n. [From Cleave to stick.] (Bot.)
   A species of Galium (Galium Aparine), having a fruit set
   with hooked bristles, which adhere to whatever they come in
   contact with; -- called also, goose grass, catchweed,
   etc.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Galium aparine
    n 1: annual having the stem beset with curved prickles; North
         America and Europe and Asia [syn: cleavers, clivers,
         goose grass, catchweed, spring cleavers, Galium
         aparine]