hydromancer vs diviner

hydromancer and diviner both are nouns.

Word	Noun	Adjective	Verb	Adverb
hydromancer	Yes	No	No	No
diviner	Yes	No	No	No

As nouns, diviner is a hypernym of hydromancer; that is, diviner is a word with a broader meaning than hydromancer:

hydromancer: one who practices hydromancy
diviner: someone who claims to discover hidden knowledge with the aid of supernatural powers

hydromancer (noun)	diviner (noun)
one who practices hydromancy	someone who claims to discover hidden knowledge with the aid of supernatural powers