bread and butter vs sustenance

bread and butter and sustenance both are nouns.

Word	Noun	Adjective	Verb	Adverb
bread and butter	Yes	No	No	No
sustenance	Yes	No	No	No

As nouns, bread and butter and sustenance are synonyms defined as:

Other synonyms of bread and butter include keep, livelihood, living, support.

bread and butter (noun)	sustenance (noun)
the financial means whereby one lives	the act of sustaining life by food or providing a means of subsistence
	a source of materials to nourish the body
	the financial means whereby one lives