acid vs acerb

acid is a noun but acerb is not a noun.

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

As adjectives, acid and acerb are synonyms defined as:

Other synonyms of acid include acerbic, acrid, bitter, blistering, caustic, sulfurous, sulphurous, virulent, vitriolic.

acid (noun)	acerb (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)	acerb (adjective)
having the characteristics of an acid	sour or bitter in taste
being sour to the taste	harsh or corrosive in tone
harsh or corrosive in tone