[L. acidum, acid]

1. Any substance that liberates hydrogen ions (protons) in solution; a hydrogen ion donor.
An acid reacts with a metal to form a salt, neutralizes bases, and turns litmus paper red.
2. A substance that can accept a pair of electrons (Lewis acid).

See: alkali; base; indicator; pH
3. A sour substance.
4. Slang term for LSD.

Subentries:
acetic acid
acetoacetic acid
acetylacetic acid
acetylsalicylic acid
acrylic acid
adenylic acid
amino acid
aminoacetic acid
aminobenzoic acid
aminocaproic acid
aminoglutaric acid
aminosalicylic acid
aminosuccinic acid
arachidonic acid
argininosuccinic acid
ascorbic acid
aspartic acid
barbituric acid
bile acid
boric acid
butyric acid
carbolic acid
carbonic acid
carboxylic acid
cholic acid
citric acid
deoxyribonucleic acid
desoxyribonucleic acid
docosahexanoic acid
eicosapenteanoic acid
essential fatty acid
ethylenediaminetetraacetic acid
fatty acid
folic acid
formic acid
formiminoglutamic acid
free fatty acid
gadolinium-diethylenetriamine pentaacetic acid
gallic acid
gammalinoleic acid
glucuronic acid
glutamic acid
glyceric acid
glycocholic acid
glycolic acid
homogentisic acid
hyaluronic acid
hydriodic acid
hydrochloric acid
hydrocyanic acid
hydrofluoric acid (HF)
hydroxy acid
hydroxy-iminodiacetic acid
hydroxybutyric acid
hydroxycitric acid
hypochlorous acid
imino acid
inorganic acid
keto acid
lactic acid
linoleic acid
linolenic acid
lysergic acid
lysophosphatidic acid
malic acid
malonic acid
mandelic acid
monounsaturated fatty acid
oleic acid
omega-6 (ω6) fatty acids
organic acid
orotic acid
oxalic acid
palmitic acid
pentanoic acid
peptide nucleic acid
perchloric acid
phenylglycolic acid
phosphoric acid
picric acid
pyruvic acid
ribonucleic acid
saturated fatty acid
silicic acid
succinic acid
sulfonic acid
sulfosalicylic acid
sulfuric acid
sulfurous acid
tannic acid
tartaric acid
taurocholic acid
unsaturated fatty acid
valeric acid
valproic acid