unsuitable vs undesirable

unsuitable is not a noun while undesirable is a noun.

Word	Noun	Adjective	Verb	Adverb
unsuitable	No	Yes	No	No
undesirable	Yes	Yes	No	No

As adjectives, unsuitable and undesirable are synonyms defined as:

unsuitable and undesirable: not worthy of being chosen (especially as a spouse)

unsuitable (noun)	undesirable (noun)
	one whose presence is undesirable

unsuitable (adjective)	undesirable (adjective)
not conducive to good moral development	not wanted
not worthy of being chosen (especially as a spouse)	not worthy of being chosen (especially as a spouse)
not meant or adapted for a particular purpose
not capable of being applied