pacer vs pacesetter

pacer and pacesetter both are nouns.

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

As nouns, pacer and pacesetter are synonyms defined as:

Other synonyms of pacer include pacemaker.

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