The Collaborative International Dictionary of English v.0.48:

Chickweed \Chick"weed`\ (-w[=e]d`), n. (Bot.)
   The name of several caryophyllaceous weeds, especially
   Stellaria media, the seeds and flower buds of which are a
   favorite food of small birds.
   [1913 Webster]

WordNet (r) 3.0 (2006):

chickweed
    n 1: any of various plants of the genus Stellaria
    2: any of various plants related to the common chickweed [syn:
       mouse-ear chickweed, mouse eared chickweed, mouse ear,
       clammy chickweed, chickweed]