loud vs loudness

loud is not a noun while loudness is a noun.

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

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

loud (adjective)	loudness (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

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