sick pay vs earnings

sick pay and earnings both are nouns.

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

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

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

sick pay (noun)	earnings (noun)
wages paid to an employee who is on sick leave	something that remunerates
	the excess of revenues over outlays in a given period of time (including depreciation and other non-cash expenses)