undertow vs undertide

undertow and undertide both are nouns.

Word	Noun	Adjective	Verb	Adverb
undertow	Yes	No	No	No
undertide	Yes	No	No	No

As nouns, undertide is a hypernym of undertow; that is, undertide is a word with a broader meaning than undertow:

undertow: the seaward undercurrent created after waves have broken on the shore
undertide: a current below the surface of a fluid

Other hypernyms of undertow include undercurrent.

undertow (noun)	undertide (noun)
the seaward undercurrent created after waves have broken on the shore	a current below the surface of a fluid
an inclination contrary to the strongest or prevailing feeling