- any of a class of sulphur-containing organic compounds with the formula RSH, where R is an organic groupAlso called (not in technical usage): mercaptan
- A mixture of sulfurated and sulfonated petroleum oils that is purified with ammonia and is used in the treatment of skin diseases.
- A sulfur-containing organic compound having the general formula RSH, where R is another element or radical. Thiols are typically very volatile and strong-smelling, and are responsible for the odor of onions, garlic, rotting flesh, and skunk musk. Also called mercaptan