loudness vs loud

loudness is a noun but loud is not a noun.

Word	Noun	Adjective	Verb	Adverb
loudness	Yes	No	No	No
loud	No	Yes	No	Yes

loudness (noun)	loud (noun)
the magnitude of sound (usually in a specified direction)
tasteless showiness

loudness (adjective)	loud (adjective)
	characterized by or producing sound of great volume or intensity
	(used chiefly as a direction or description in music) indicating that said piece or segment should be played loudly
	tastelessly showy

loudness (adverb)	loud (adverb)
	with relatively high volume