1. (n.) A substance that can neutralize a base and is sour, sharp, or biting to the taste\.

2. (a.) of or pertaining to an acid; as, acid reaction.

3. (n.) A sour substance.

4. (n.) One of a class of compounds, generally but not always distinguished by their sour taste, solubility in water, and reddening of vegetable blue or violet colors. They are also characterized by the power of destroying the distinctive properties of alkalis or bases, combining with them to form salts, at the same time losing their own peculiar properties. They all contain hydrogen, united with a more negative element or radical, either alone, or more generally with oxygen, and take their names from this negative element or radical. Those which contain no oxygen are sometimes called hydracids in distinction from the others which are called oxygen acids or oxacids.

DET DMT Foamite LSD Mary Jane STP THC acerb acerbate acerbic acerbity acetic acetose acetous acetylsalicylic acid acid acidic acidity acidulant acidulated acidulent acidulous acidulousness acrid acrimonious acrimony actual cautery agent alkali alkalinity alloisomer amino acid ammono acid angry animosity anion antacid antidepressant aqua fortis aqua regia arsenic acid ascorbic acid asperity asperous aspirin astringent ataractic atom automatic sprinkler base basic battery acid benzoic acid bile biochemical biting bitter bitter resentment bitterness bitterness of spirit boric acid brand brand iron branding iron bread-and-butter pickle burning butyric acid carbolic acid carbon tet carbon tetrachloride carbon-dioxide foam carbonic acid cation caustic causticity cauter cauterant cauterizer cautery chemical chemical element chemicobiological chemicoengineering chemicomineralogical chemicophysical chemurgic chloric acid chlorous acid chokecherry choler choleric chromic acid chromoisomer citric acid compound copolymer copolymeric copolymerous corroding corrosive crab apple cutting cyanic acid deck gun deluge set diethyltryptamine dill pickle dimer dimeric dimerous dimethyltryptamine discontented double-edged driving dry edged effective electrocautery electrochemical element elemental elementary embittered escharotic extinguisher feeling evil fierce fire apparatus fire engine fire hose fire hydrant fireplug fluoric acid foam foam extinguisher forceful forcible formic acid gage gall ganja gnashing of teeth grass green apple gutsy hallucinogen hard feelings harsh hash hashish hay heartburning heavy chemicals hemp heteromerous high polymer homopolymer hook-and-ladder hot iron hydracid hydrochloric acid hydrocyanic acid hyperacid hypochlorous acid imperative impressive incisive inorganic chemical ion irritating isomer isomerous joint kava keen lactic acid ladder pipe lemon lignosulphonic acid lime lunar caustic macrochemical macromolecule malic acid marijuana mescal mescal bean mescal button mescaline metamer metameric mind-altering drug mind-blowing drug mind-expanding drug molecule monomer monomerous mordacious mordant morning glory seeds moxa muriatic acid nervous neutralizer niacin nicotinic acid nonacid nose-tickling oil of vitriol organic chemical out of humor out of sorts out of temper oxalic acid oxyacid pectic acid penetrating perboric acid perchloric acid peyote phenol phosphoric acid photochemical physicochemical phytochemical pickle picric acid piercing piquant poignant polymer polymeric pot potential cautery powerful prussic acid pseudoisomer psilocin psilocybin psychedelic psychic energizer psychoactive drug psychochemical psychotomimetic pumper punchy pungent radical radiochemical radium rancor rancorous rankled rankling