pacer vs pacemaker

pacer and pacemaker both are nouns.

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

As nouns, pacer and pacemaker are synonyms defined as:

Other synonyms of pacer include pacesetter.

pacer (noun)	pacemaker (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	an implanted electronic device that takes over the function of the natural cardiac pacemaker
	a specialized bit of heart tissue that controls the heartbeat
	a leading instance in its field