oilman vs man of affairs

oilman and man of affairs both are nouns.

Word	Noun	Adjective	Verb	Adverb
oilman	Yes	No	No	No
man of affairs	Yes	No	No	No

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

oilman: a person who owns or operates oil wells
man of affairs: a person engaged in commercial or industrial business (especially an owner or executive)

Other hypernyms of oilman include businessman.

oilman (noun)	man of affairs (noun)
a worker who produces or sells petroleum	a person engaged in commercial or industrial business (especially an owner or executive)
a person who owns or operates oil wells