The Collaborative International Dictionary of English v.0.48:

Cockcrow \Cock"crow\, Cockcrowing \Cock"crow`ing\, n.
   The time at which cocks first crow; the early morning; the
   first light of day.

   Syn: dawn, dawning, morning, aurora, first light, daybreak,
        break of day, break of the day, dayspring, sunrise,
        sunup.
        [1913 Webster + WordNet 1.5]

WordNet (r) 3.0 (2006):

cockcrow
    n 1: the first light of day; "we got up before dawn"; "they
         talked until morning" [syn: dawn, dawning, morning,
         aurora, first light, daybreak, break of day, break
         of the day, dayspring, sunrise, sunup, cockcrow]
         [ant: sundown, sunset]