oilman vs rigger

oilman and rigger both are nouns.

Word	Noun	Adjective	Verb	Adverb
oilman	Yes	No	No	No
rigger	Yes	No	No	No

As nouns, rigger is a hyponym of oilman; that is, rigger is a word with a more specific, narrower meaning than oilman:

Other hyponyms of oilman include oil rigger.

oilman (noun)	rigger (noun)
a worker who produces or sells petroleum	a long slender pointed sable brush used by artists
a person who owns or operates oil wells	a sailing vessel with a specified rig
	someone who rigs ships
	someone who works on an oil rig