quick buck vs lucre

quick buck and lucre both are nouns.

Word	Noun	Adjective	Verb	Adverb
quick buck	Yes	No	No	No
lucre	Yes	No	No	No

As nouns, lucre is a hypernym of quick buck; that is, lucre is a word with a broader meaning than quick buck:

quick buck: quick or easy earnings
lucre: the excess of revenues over outlays in a given period of time (including depreciation and other non-cash expenses)

Other hypernyms of quick buck include earnings, net, net income, net profit, profit, profits.

quick buck (noun)	lucre (noun)
quick or easy earnings	the excess of revenues over outlays in a given period of time (including depreciation and other non-cash expenses)
	informal terms for money