The Collaborative International Dictionary of English v.0.48:

Daybreak \Day"break`\ (d[=a]"br[=a]k`), n.
   The time of the first appearance of light in the morning.
   [1913 Webster]

WordNet (r) 3.0 (2006):

daybreak
    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]

Moby Thesaurus II by Grady Ward, 1.0:

21 Moby Thesaurus words for "daybreak":
   aurora, break of day, brightening, chanticleer, cockcrow,
   cocklight, crack of dawn, dawn, dawning, day-peep, daylight,
   dayspring, first brightening, light, morn, morning, peep of day,
   prime, sunrise, sunup, vestibule of Day