oilman vs skilled worker

oilman and skilled worker both are nouns.

Word	Noun	Adjective	Verb	Adverb
oilman	Yes	No	No	No
skilled worker	Yes	No	No	No

As nouns, skilled worker is a hypernym of oilman; that is, skilled worker is a word with a broader meaning than oilman:

Other hypernyms of oilman include skilled workman, trained worker.

oilman (noun)	skilled worker (noun)
a worker who produces or sells petroleum	a worker who has acquired special skills
a person who owns or operates oil wells