improbable vs unlikely

improbable and unlikely both are adjectives.

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

As adjectives, improbable and unlikely are synonyms defined as:

improbable and unlikely: not likely to be true or to occur or to have occurred

As adjectives, improbable and unlikely are synonyms defined as:

Other synonyms of improbable include unbelievable, unconvincing.

improbable (adjective)	unlikely (adjective)
not likely to be true or to occur or to have occurred	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
too improbable to admit of belief	having a probability too low to inspire belief