half-pay vs earnings

half-pay and earnings both are nouns.

Word	Noun	Adjective	Verb	Adverb
half-pay	Yes	No	No	No
earnings	Yes	No	No	No

As nouns, earnings is a hypernym of half-pay; that is, earnings is a word with a broader meaning than half-pay:

Other hypernyms of half-pay include pay, remuneration, salary, wage.

half-pay (noun)	earnings (noun)
reduced wage paid to someone who is not working full time	something that remunerates
	the excess of revenues over outlays in a given period of time (including depreciation and other non-cash expenses)