redundancy vs plethora

redundancy and plethora both are nouns.

Word	Noun	Adjective	Verb	Adverb
redundancy	Yes	No	No	No
plethora	Yes	No	No	No

As nouns, plethora is a hypernym of redundancy; that is, plethora is a word with a broader meaning than redundancy:

Other hypernyms of redundancy include embarrassment, overplus, superfluity.

redundancy (noun)	plethora (noun)
repetition of an act needlessly	extreme excess
the attribute of being superfluous and unneeded
(electronics) a system design that duplicates components to provide alternatives in case one component fails
repetition of messages to reduce the probability of errors in transmission