service man vs maintenance man

service man and maintenance man both are nouns.

Word	Noun	Adjective	Verb	Adverb
service man	Yes	No	No	No
maintenance man	Yes	No	No	No

As nouns, service man and maintenance man are synonyms defined as:

service man and maintenance man: a skilled worker whose job is to repair things

Other synonyms of service man include repairman.

service man (noun)	maintenance man (noun)
a skilled worker whose job is to repair things	a skilled worker whose job is to repair things