undertide vs tide

undertide and tide both are nouns.

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

undertide (noun)	tide (noun)
a current below the surface of a fluid	the periodic rise and fall of the sea level under the gravitational pull of the moon
	something that may increase or decrease (like the tides of the sea)
	there are usually two high and two low tides each day