first-rater vs worker

first-rater and worker both are nouns.

Word	Noun	Adjective	Verb	Adverb
first-rater	Yes	No	No	No
worker	Yes	No	No	No

As nouns, worker is a hypernym of first-rater; that is, worker is a word with a broader meaning than first-rater:

Other hypernyms of first-rater include actor, doer.

first-rater (noun)	worker (noun)
one who is first-rate	sterile member of a colony of social insects that forages for food and cares for the larvae
	a person who works at a specific occupation
	a member of the working class (not necessarily employed)
	a person who acts and gets things done