The Collaborative International Dictionary of English v.0.48:

Catchfly \Catch"fly\, n. (Bot.)
   A plant with the joints of the stem, and sometimes other
   parts, covered with a viscid secretion to which small insects
   adhere. The species of Silene are examples of the catchfly.
   [1913 Webster]

WordNet (r) 3.0 (2006):

catchfly
    n 1: any plant of the genus Silene [syn: silene, campion,
         catchfly]
    2: mostly perennial herbs with sticky stems that catch insects;
       widespread in north temperate zone [syn: lychnis,
       catchfly]