break of day vs morning

break of day and morning both are nouns.

Word	Noun	Adjective	Verb	Adverb
break of day	Yes	No	No	No
morning	Yes	No	No	No

As nouns, break of day and morning are synonyms defined as:

Other synonyms of break of day include aurora, break of the day, cockcrow, dawn, dawning, daybreak, dayspring, first light, sunrise, sunup.

break of day (noun)	morning (noun)
the first light of day	a conventional expression of greeting or farewell, used to wish someone a good morning
	the earliest period
	the time period between dawn and noon
	the first light of day