springtide vs highwater

springtide and highwater both are nouns.

Word	Noun	Adjective	Verb	Adverb
springtide	Yes	No	No	No
highwater	Yes	No	No	No

As nouns, highwater is a hypernym of springtide; that is, highwater is a word with a broader meaning than springtide:

springtide: a greater than average tide occurring during the new and full moons
highwater: the tide when the water is highest

Other hypernyms of springtide include high tide, high water.

springtide (noun)	highwater (noun)
a greater than average tide occurring during the new and full moons	the tide when the water is highest
a swelling rush of anything