off-the-wall vs eccentric

off-the-wall is not a noun while eccentric is a noun.

Word	Noun	Adjective	Verb	Adverb
off-the-wall	No	Yes	No	No
eccentric	Yes	Yes	No	No

As adjectives, off-the-wall and eccentric are synonyms defined as:

off-the-wall and eccentric: conspicuously or grossly unconventional or unusual

Other synonyms of off-the-wall include bizarre, flakey, flaky, freakish, freaky, gonzo, outlandish, outre.

off-the-wall (noun)	eccentric (noun)
	a person with an unusual or odd personality
	a person of a specified kind (usually with many eccentricities)

off-the-wall (adjective)	eccentric (adjective)
conspicuously or grossly unconventional or unusual	not having a common center; not concentric
	conspicuously or grossly unconventional or unusual