In layman's terms, the word<unk>  (Arabic:الكحل al-kuḥl) usually refers to ethanol, also known as grain<unk>  or (older) spirits of wine, or to any<unk> ic 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.) Ethanol is the most widely used depressant in the world, and has been for thousands of years. This sense underlies the term<unk> ism (addiction to<unk> .
In chemistry, an<unk>  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<unk>  is CnH2n+1OH.
Other<unk> s are usually described with a clarifying adjective, as in isopropyl<unk>  (propan-2-ol) or wood<unk>  (methyl<unk> , or methanol).  The suffix -ol appears in the "official" IUPAC chemical name of all<unk> s.
There are three major, subsets of<unk> s: 'primary' (1°), 'secondary' (2°) and 'tertiary' (3°), based upon the number of carbons the C-OH carbon (shown in red) is bonded to. Ethanol is a simple 'primary'<unk> . The simplest secondary<unk>  is isopropyl<unk>  (propan-2-ol), and a simple tertiary<unk>  is tert-butyl<unk>  (2-methylpropan-2-ol).
The phenols with<unk> rent compound phenol have a hydroxyl group (attached to a benzene ring) just like<unk> s, but differ sufficiently in properties as to warrant a separate treatment.
Carbohydrates (sugars) and sugar<unk> s are an important class of compounds containing multiple<unk>  functional groups. For example, sucrose (common sugar) contains eight hydroxyl groups per molecule and sorbitol has six. Most of the attributes of these polyols, from nomenclature, to occurrence, use and toxicity, are sufficiently different from simple aliphatic<unk> s as to require a separate treatment.
Alcohol
Tobacco
Cannabis 
Polychlorinated biphenyl
Nicotine 
Nicotine
Opiate
Heroin