The Collaborative International Dictionary of English v.0.48:

Cornflower \Corn"flow`er\ (k[^o]rn"flou`[~e]r), n. (Bot.)
   A conspicuous wild flower (Centaurea Cyanus), growing in
   grainfields.
   [1913 Webster]

WordNet (r) 3.0 (2006):

cornflower
    n 1: plant of southern and southeastern United States grown for
         its yellow flowers that can be dried [syn: strawflower,
         cornflower, Uvularia grandiflora]
    2: an annual Eurasian plant cultivated in North America having
       showy heads of blue or purple or pink or white flowers [syn:
       cornflower, bachelor's button, bluebottle, Centaurea
       cyanus]