linear vs linearity

linear is not a noun while linearity is a noun.

Word	Noun	Adjective	Verb	Adverb
linear	No	Yes	No	No
linearity	Yes	No	No	No

linear (noun)	linearity (noun)
	the property of having one dimension

linear (adjective)	linearity (adjective)
of or in or along or relating to a line; involving or having a single dimension
designating or involving an equation whose terms are of the first degree
of a circuit or device having an output that is proportional to the input
measured lengthwise
(of a leaf shape) long and narrow