busyness vs busy

busyness is a noun but busy is not a noun.

Word	Noun	Adjective	Verb	Adverb
busyness	Yes	No	No	No
busy	No	Yes	Yes	No

busyness (noun)	busy (noun)
the state of being or appearing to be actively engaged in an activity

busyness (adjective)	busy (adjective)
	actively or fully engaged or occupied
	overcrowded or cluttered with detail
	intrusive in a meddling or offensive manner
	(of facilities such as telephones or lavatories) unavailable for use by anyone else or indicating unavailability; (`engaged' is a British term for a busy telephone line)
	crowded with or characterized by much activity

busyness (verb)	busy (verb)
	keep busy with