improbable vs marvellous

improbable and marvellous both are adjectives.

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

As adjectives, improbable and marvellous are synonyms defined as:

Other synonyms of improbable include marvelous, tall.

improbable (adjective)	marvellous (adjective)
not likely to be true or to occur or to have occurred	extraordinarily good or great; used especially as intensifiers
having a probability too low to inspire belief	too improbable to admit of belief
too improbable to admit of belief	being or having the character of a miracle