Daybreak is the first light of the morning. At daybreak, before daybreak, from daybreak to dusk.
It is the moment light first appears, before the sun itself, so daybreak comes earlier than sunrise — by about half an hour in Britain, and much more at high latitudes. Dawn is the near-synonym and is commoner; daybreak is slightly more literary. Note that the phrase pictures the day breaking through the dark, which is the same image as in the German Tagesanbruch and the French point du jour.
1noundaybreakThe first light of the morning.
“They left at daybreak, about four in the morning.”
daybreak is a time of day.
Day plus break, a plain English compound from the sixteenth century. The image of light breaking through is shared with several other European languages, each having built it separately.
From day + break.
Etymology from Wiktionary, CC BY-SA