1. 
[syn: dawn, dawning, morning, aurora, first light, daybreak, break of day, break of the day, dayspring, sunrise, sunup, cockcrow]
WordNet (r) 3.0 (2006):
break of day
    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:
18 Moby Thesaurus words for "break of day":
   aurora, brightening, chanticleer, cocklight, crack of dawn, dawn,
   dawning, day-peep, daybreak, daylight, dayspring,
   first brightening, light, peep of day, prime, sunrise, sunup,
   vestibule of Day