piece rate vs earnings

piece rate and earnings both are nouns.

Word	Noun	Adjective	Verb	Adverb
piece rate	Yes	No	No	No
earnings	Yes	No	No	No

As nouns, earnings is a hypernym of piece rate; that is, earnings is a word with a broader meaning than piece rate:

Other hypernyms of piece rate include pay, remuneration, salary, wage.

piece rate (noun)	earnings (noun)
a fixed rate paid according to the quantity produced.	something that remunerates
	the excess of revenues over outlays in a given period of time (including depreciation and other non-cash expenses)