gentleman-at-arms vs gentleman

gentleman-at-arms and gentleman both are nouns.

Word	Noun	Adjective	Verb	Adverb
gentleman-at-arms	Yes	No	No	No
gentleman	Yes	No	No	No

As nouns, gentleman is a hypernym of gentleman-at-arms; that is, gentleman is a word with a broader meaning than gentleman-at-arms:

gentleman-at-arms: one of 40 gentlemen who attend the British sovereign on state occasions
gentleman: a man of refinement

gentleman-at-arms (noun)	gentleman (noun)
one of 40 gentlemen who attend the British sovereign on state occasions	a man of refinement
	a manservant who acts as a personal attendant to his employer