eccentric vs off-the-wall

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

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

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

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

Other synonyms of eccentric include bizarre, flakey, flaky, freakish, freaky, gonzo, outlandish, outre.

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

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