undertide vs sea-puss

undertide and sea-puss both are nouns.

Word	Noun	Adjective	Verb	Adverb
undertide	Yes	No	No	No
sea-puss	Yes	No	No	No

As nouns, sea-puss is a hyponym of undertide; that is, sea-puss is a word with a more specific, narrower meaning than undertide:

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

Other hyponyms of undertide include sea-poose, sea-purse, sea purse, sea puss, undertow.

undertide (noun)	sea-puss (noun)
a current below the surface of a fluid	the seaward undercurrent created after waves have broken on the shore