undertow vs undercurrent

undertow and undercurrent both are nouns.

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

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

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

Other hypernyms of undertow include undertide.

undertow (noun)	undercurrent (noun)
the seaward undercurrent created after waves have broken on the shore	a subdued emotional quality underlying an utterance; implicit meaning
an inclination contrary to the strongest or prevailing feeling	a current below the surface of a fluid