acid vs unpleasant

acid is a noun but unpleasant is not a noun.

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

acid (noun)	unpleasant (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

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