nadir vs hardship

nadir and hardship both are nouns.

Word	Noun	Adjective	Verb	Adverb
nadir	Yes	No	No	No
hardship	Yes	No	No	No

As nouns, hardship is a hypernym of nadir; that is, hardship is a word with a broader meaning than nadir:

Other hypernyms of nadir include adversity, hard knocks.

nadir (noun)	hardship (noun)
the point below the observer that is directly opposite the zenith on the imaginary sphere against which celestial bodies appear to be projected	something hard to endure
an extreme state of adversity; the lowest point of anything	something that causes or entails suffering
	a state of misfortune or affliction