lineman vs gaffer

lineman and gaffer both are nouns.

Word	Noun	Adjective	Verb	Adverb
lineman	Yes	No	No	No
gaffer	Yes	No	No	No

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

lineman (noun)	gaffer (noun)
(American football) the position of a player on a football team who is stationed on the line of scrimmage	a person who exercises control over workers
one of the players on the line of scrimmage	an elderly man
a person who installs or repairs electrical or telephone lines	an electrician responsible for lighting on a movie or tv set
the surveyor who marks positions with a range pole