robustness vs robust

robustness is a noun but robust is not a noun.

Word	Noun	Adjective	Verb	Adverb
robustness	Yes	No	No	No
robust	No	Yes	No	No

robustness (noun)	robust (noun)
the property of being strong and healthy in constitution
the characteristic of being strong enough to withstand intellectual challenge

robustness (adjective)	robust (adjective)
	sturdy and strong in form, constitution, or construction
	strong enough to withstand or overcome intellectual challenges or adversity
	marked by richness and fullness of flavor
	rough and crude