neap vs high water

neap and high water both are nouns.

Word	Noun	Adjective	Verb	Adverb
neap	Yes	No	No	No
high water	Yes	No	No	No

As nouns, high water is a hypernym of neap; that is, high water is a word with a broader meaning than neap:

neap: a less than average tide occurring at the first and third quarters of the moon
high water: the tide when the water is highest

Other hypernyms of neap include high tide, highwater.

neap (noun)	high water (noun)
a less than average tide occurring at the first and third quarters of the moon	the tide when the water is highest