quick buck vs net income

quick buck and net income both are nouns.

Word	Noun	Adjective	Verb	Adverb
quick buck	Yes	No	No	No
net income	Yes	No	No	No

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

quick buck: quick or easy earnings
net income: 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, lucre, net, net profit, profit, profits.

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