oilman vs trained worker

oilman and trained worker both are nouns.

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

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

Other hypernyms of oilman include skilled worker, skilled workman.

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