workman vs working man

workman and working man both are nouns.

Word	Noun	Adjective	Verb	Adverb
workman	Yes	No	No	No
working man	Yes	No	No	No

As nouns, workman and working man are synonyms defined as:

workman and working man: an employee who performs manual or industrial labor

Other synonyms of workman include working person, workingman.

workman (noun)	working man (noun)
an employee who performs manual or industrial labor	an employee who performs manual or industrial labor