undesirable vs unsuitable

undesirable is a noun but unsuitable is not a noun.

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

As adjectives, undesirable and unsuitable are synonyms defined as:

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

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

undesirable (adjective)	unsuitable (adjective)
not wanted	not conducive to good moral development
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