unbelievable vs unlikely

unbelievable and unlikely both are adjectives.

Word	Noun	Adjective	Verb	Adverb
unbelievable	No	Yes	No	No
unlikely	No	Yes	No	No

As adjectives, unbelievable and unlikely are synonyms defined as:

unbelievable and unlikely: having a probability too low to inspire belief

Other synonyms of unbelievable include improbable, unconvincing.

unbelievable (adjective)	unlikely (adjective)
beyond belief or understanding	has little chance of being the case or coming about
having a probability too low to inspire belief	not likely to be true or to occur or to have occurred
	having a probability too low to inspire belief