dead ringer vs ringer

dead ringer and ringer both are nouns.

Word	Noun	Adjective	Verb	Adverb
dead ringer	Yes	No	No	No
ringer	Yes	No	No	No

As nouns, dead ringer and ringer are synonyms defined as:

Other synonyms of dead ringer include clone.

dead ringer (noun)	ringer (noun)
a person who is almost identical to another	(horseshoes) the successful throw of a horseshoe or quoit so as to encircle a stake or peg
	a contestant entered in a competition under false pretenses
	a person who is almost identical to another
	a person who rings church bells (as for summoning the congregation)