Chemistry. a compound usually having a sour taste and capable of neutralizing alkalis and reddening blue litmus paper, containing hydrogen that can be replaced by a metal or an electropositive group to form a salt, or containing an atom that can accept a pair of electrons from a base. Acids are proton donors that yield hydronium ions in water solution, or electron-pair acceptors that combine with electron-pair donors or bases.
a substance with a sour taste.
something, as a remark or piece of writing, that is sharp, sour, or ill-natured: His criticism was pure acid.
Slang. LSD (def 2).
Chemistry. belonging or pertaining to acids or the anhydrides of acids. having only a part of the hydrogen of an acid replaced by a metal or its equivalent: an acid phosphate. having a pH value of less than 7. Compare alkaline (def 4).