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 ) .

sharp or biting to the taste; tasting like vinegar; sour

acid fruits.

sharp, biting, or ill-natured in mood, manner, etc.

an acid remark; an acid wit.

Geology . containing much silica.

Metallurgy . noting, pertaining to, or made by a process in which the lining of the furnace, or the slag that is present, functions as an acid in high-temperature reactions in taking electrons from oxide ions

usually a siliceous material, as sand or ganister. Compare basic def. 3

put on the acid, Australian Slang . to importune someone, as for money, sexual favors

or confidential information.