gentleman vs gentleman's gentleman

gentleman and gentleman's gentleman both are nouns.

Word	Noun	Adjective	Verb	Adverb
gentleman	Yes	No	No	No
gentleman's gentleman	Yes	No	No	No

As nouns, gentleman and gentleman's gentleman are synonyms defined as:

gentleman and gentleman's gentleman: a manservant who acts as a personal attendant to his employer

Other synonyms of gentleman include man, valet, valet de chambre.

gentleman (noun)	gentleman's gentleman (noun)
a man of refinement	a manservant who acts as a personal attendant to his employer
a manservant who acts as a personal attendant to his employer