unpleasant vs acid

unpleasant is not a noun while acid is a noun.

Word	Noun	Adjective	Verb	Adverb
unpleasant	No	Yes	No	No
acid	Yes	Yes	No	No

unpleasant (noun)	acid (noun)
	street name for lysergic acid diethylamide
	any of various water-soluble compounds having a sour taste and capable of turning litmus red and reacting with a base to form a salt

unpleasant (adjective)	acid (adjective)
offensive or disagreeable; causing discomfort or unhappiness	having the characteristics of an acid
	being sour to the taste
	harsh or corrosive in tone