computing vs on-line

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

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

computing (noun)	on-line (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

computing (adjective)	on-line (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