improbable vs tall

improbable is not a noun while tall is a noun.

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

As adjectives, improbable and tall are synonyms defined as:

Other synonyms of improbable include marvellous, marvelous.

improbable (noun)	tall (noun)
	a garment size for a tall person

improbable (adjective)	tall (adjective)
not likely to be true or to occur or to have occurred	great in vertical dimension; high in stature
having a probability too low to inspire belief	impressively difficult
too improbable to admit of belief	too improbable to admit of belief
	lofty in style
	having a specified height