fast buck vs profit

fast buck and profit both are nouns.

Word	Noun	Adjective	Verb	Adverb
fast buck	Yes	No	No	No
profit	Yes	No	Yes	No

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

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

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

fast buck (noun)	profit (noun)
quick or easy earnings	the advantageous quality of being beneficial
	the excess of revenues over outlays in a given period of time (including depreciation and other non-cash expenses)

fast buck (verb)	profit (verb)
	make a profit; gain money or materially
	derive a benefit from