loudly vs loud

loudly is not an adjective while loud is an adjective.

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

As adverbs, loudly and loud are synonyms defined as:

Other synonyms of loudly include aloud.

loudly (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

loudly (adverb)	loud (adverb)
with relatively high volume	with relatively high volume
used as a direction in music; to be played relatively loudly
in manner that attracts attention