pacesetter vs pacer

pacesetter and pacer both are nouns.

Word	Noun	Adjective	Verb	Adverb
pacesetter	Yes	No	No	No
pacer	Yes	No	No	No

As nouns, pacesetter and pacer are synonyms defined as:

Other synonyms of pacesetter include pacemaker.

pacesetter (noun)	pacer (noun)
a horse used to set the pace in racing	a horse trained to a special gait in which both feet on one side leave the ground together
a leading instance in its field	a horse used to set the pace in racing