elusive vs elusiveness

elusive is not a noun while elusiveness is a noun.

Word	Noun	Adjective	Verb	Adverb
elusive	No	Yes	No	No
elusiveness	Yes	No	No	No

elusive (noun)	elusiveness (noun)
	the quality of being difficult to grasp or pin down

elusive (adjective)	elusiveness (adjective)
skillful at eluding capture
making great mental demands; hard to comprehend or solve or believe
difficult to detect or grasp by the mind or analyze
difficult to describe