nadir vs low-water mark

nadir and low-water mark both are nouns.

Word	Noun	Adjective	Verb	Adverb
nadir	Yes	No	No	No
low-water mark	Yes	No	No	No

As nouns, nadir and low-water mark are synonyms defined as:

nadir and low-water mark: an extreme state of adversity; the lowest point of anything

nadir (noun)	low-water mark (noun)
the point below the observer that is directly opposite the zenith on the imaginary sphere against which celestial bodies appear to be projected	a line marking the lowest level reached
an extreme state of adversity; the lowest point of anything	an extreme state of adversity; the lowest point of anything