robust vs robustness

robust is not a noun while robustness is a noun.

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

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

robust (adjective)	robustness (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