ebb vs ebb away

ebb is a noun but ebb away is not a noun.

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

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

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

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

ebb (verb)	ebb away (verb)
fall away or decline	flow back or recede
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