ebb down vs ebb

ebb down is not a noun while ebb is a noun.

Word	Noun	Adjective	Verb	Adverb
ebb down	No	No	Yes	No
ebb	Yes	No	Yes	No

As verbs, ebb down and ebb are synonyms defined as:

Other synonyms of ebb down include ebb away, ebb off, ebb out.

ebb down (noun)	ebb (noun)
	the outward flow of the tide
	a gradual decline (in size or strength or power or number)

ebb down (verb)	ebb (verb)
flow back or recede	fall away or decline
	hem in fish with stakes and nets so as to prevent them from going back into the sea with the ebb
	flow back or recede