The Collaborative International Dictionary of English v.0.48:

cow-cockle \cow-cockle\ n.
   a European annual (Vaccaria hispanica) with pale
   rose-colored flowers; cultivated flower or self-sown
   grainfield weed; introduced in North America; sometimes
   classified as a soapwort.

   Syn: cowherb, cow cockle, Vaccaria hispanica, Vaccaria
        pyramidata, Saponaria vaccaria.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Vaccaria hispanica
    n 1: European annual with pale rose-colored flowers; cultivated
         flower or self-sown grainfield weed; introduced in North
         America; sometimes classified as a soapwort [syn:
         cowherb, cow cockle, Vaccaria hispanica, Vaccaria
         pyramidata, Saponaria vaccaria]