fifth wheel vs redundancy

fifth wheel and redundancy both are nouns.

Word	Noun	Adjective	Verb	Adverb
fifth wheel	Yes	No	No	No
redundancy	Yes	No	No	No

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

Other hypernyms of fifth wheel include redundance.

fifth wheel (noun)	redundancy (noun)
a steering bearing that enables the front axle of a horse-drawn wagon to rotate	repetition of an act needlessly
an extra car wheel and tire for a four-wheel vehicle	the attribute of being superfluous and unneeded
someone or something that is unwanted 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