acerb vs acid

acerb is not a noun while acid is a noun.

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

As adjectives, acerb and acid are synonyms defined as:

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

acerb (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

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