ringer vs sham

ringer and sham both are nouns.

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

As nouns, sham is a hypernym of ringer; that is, sham is a word with a broader meaning than ringer:

Other hypernyms of ringer include fake, faker, fraud, imposter, impostor, pretender, pseud, pseudo, role player, shammer.

ringer (noun)	sham (noun)
(horseshoes) the successful throw of a horseshoe or quoit so as to encircle a stake or peg	something that is a counterfeit; not what it seems to be
a contestant entered in a competition under false pretenses	a person who makes deceitful pretenses
a person who is almost identical to another
a person who rings church bells (as for summoning the congregation)

ringer (adjective)	sham (adjective)
	adopted in order to deceive

ringer (verb)	sham (verb)
	make believe with the intent to deceive
	make a pretence of