upbeat vs offbeat

upbeat and offbeat both are nouns.

Word	Noun	Adjective	Verb	Adverb
upbeat	Yes	Yes	No	No
offbeat	Yes	Yes	No	No

As nouns, upbeat and offbeat are synonyms defined as:

upbeat and offbeat: an unaccented beat (especially the last beat of a measure)

upbeat (noun)	offbeat (noun)
an unaccented beat (especially the last beat of a measure)	an unaccented beat (especially the last beat of a measure)
a contented state of being happy and healthy and prosperous

upbeat (adjective)	offbeat (adjective)
pleasantly (even unrealistically) optimistic	(informal) strikingly unconventional