maintenance vs bread and butter

maintenance and bread and butter both are nouns.

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

As nouns, bread and butter is a hypernym of maintenance; that is, bread and butter is a word with a broader meaning than maintenance:

Other hypernyms of maintenance include keep, livelihood, living, support, sustenance.

maintenance (noun)	bread and butter (noun)
activity involved in maintaining something in good working order	the financial means whereby one lives
the act of sustaining life by food or providing a means of subsistence
the unauthorized interference in a legal action by a person having no interest in it (as by helping one party with money or otherwise to continue the action) so as to obstruct justice or promote unnecessary litigation or unsettle the peace of the community
means of maintenance of a family or group
court-ordered support paid by one spouse to another after they are separated