on-line vs computing

on-line is not a noun while computing is a noun.

Word	Noun	Adjective	Verb	Adverb
on-line	No	Yes	No	No
computing	Yes	No	No	No

on-line (noun)	computing (noun)
	the procedure of calculating; determining something by mathematical or logical methods
	the branch of engineering science that studies (with the aid of computers) computable processes and structures

on-line (adjective)	computing (adjective)
connected to a computer network or accessible by computer
on a regular route of a railroad or bus or airline system
being in progress now