In chemistry, an alcohol is any organic compound in which a hydroxyl group (-OH) is bound to a carbon atom of an alkyl or substituted alkyl group. The general formula for a simple acyclic alcohol is C_nH_2n+1OH.

The word alcohol was introduced into the English language circa 1543 from the , "al-ġuḥl". In layman's terms, it usually refers to ethanol, also known as grain alcohol or (older) spirits of wine, or to any alcoholic beverage. Ethanol is a colorless, volatile liquid with a mild odor which can be obtained by the fermentation of sugars. (Industrially, it is more commonly obtained by ethylene hydration—the reaction of ethylene with water in the presence of phosphoric acid.Lodgsdon, J.E. (1994). "Ethanol." In J.I. Kroschwitz (Ed.) Encyclopedia of Chemical Technology, 4th ed. vol. 9, p. 820. New York: John Wiley & Sons.) Ethanol is the most widely used depressant in the world, and has been for thousands of years. This sense underlies the term alcoholism (addiction to alcohol).

Other alcohols are usually described with a clarifying adjective, as in isopropyl alcohol (propan-2-ol) or wood alcohol (methyl alcohol, or methanol). The suffix -ol appears in the "official" IUPAC chemical name of all alcohols.

There are three major subsets of alcohols: primary (1°), secondary (2°) and tertiary (3°), based upon the number of carbon atoms the C-OH group's carbon (shown in red) is bonded to. Ethanol is a simple 'primary' alcohol. The simplest secondary alcohol is isopropyl alcohol (propan-2-ol), and a simple tertiary alcohol is tert-butyl alcohol (2-methylpropan-2-ol).

Simple alcohols

The simplest and most commonly used alcohols are methanol and ethanol. Methanol was formerly obtained by the distillation of wood and called "wood alcohol." It is now a cheap commodity, the chemical product of carbon monoxide reacting with hydrogen under high pressure.Fact: date=September 2007 Methanol is intoxicating but not directly poisonous. It is toxic by its breakdown (toxication) by the enzyme alcohol dehydrogenase in the liver by forming formic acid and formaldehyde which cause permanent blindness by destruction of the optic nerve.

Apart from its familiar role in alcoholic beverages, ethanol is also used as a highly controlled industrial solvent and raw material. To avoid the high taxes on ethanol for consumption, additives are added to make it unpalatable (such as denatonium benzoate—"Bitrex") or poisonous (such as methanol). Ethanol in this form is known generally as denatured alcohol; when methanol is used, it may be referred to as methylated spirits ("Meths") or "surgical spirits".