combat pay vs earnings

combat pay and earnings both are nouns.

Word	Noun	Adjective	Verb	Adverb
combat pay	Yes	No	No	No
earnings	Yes	No	No	No

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

Other hypernyms of combat pay include pay, remuneration, salary, wage.

combat pay (noun)	earnings (noun)
extra pay for soldiers engaged in active combat	something that remunerates
	the excess of revenues over outlays in a given period of time (including depreciation and other non-cash expenses)