knight bachelor vs bachelor-at-arms

knight bachelor and bachelor-at-arms both are nouns.

Word	Noun	Adjective	Verb	Adverb
knight bachelor	Yes	No	No	No
bachelor-at-arms	Yes	No	No	No

As nouns, knight bachelor and bachelor-at-arms are synonyms defined as:

knight bachelor and bachelor-at-arms: a knight of the lowest order; could display only a pennon

Other synonyms of knight bachelor include bachelor.

knight bachelor (noun)	bachelor-at-arms (noun)
a knight of the lowest order; could display only a pennon	a knight of the lowest order; could display only a pennon