big vs bigness

big is not a noun while bigness is a noun.

Word	Noun	Adjective	Verb	Adverb
big	No	Yes	No	Yes
bigness	Yes	No	No	No

big (noun)	bigness (noun)
	the property of having a relatively great size

big (adjective)	bigness (adjective)
above average in size or number or quantity or magnitude or extent
conspicuous in position or importance
given or giving freely
generous and understanding and tolerant
marked by intense physical force
significant
prodigious
serious or severe
loud and firm
(of animals) fully developed
in an advanced stage of pregnancy
feeling self-importance
exhibiting self-importance