A paint thinner is a solvent used to thin oil-based paints. Solvents labeled "paint thinner" are usually mineral spirits having a flash point at about 40 °C, the same as some popular brands of charcoal starter.

A thinner is a volatile solvent that is used to dilute or extend oil-based paints or cleanup after use. Common solvents used as paint thinner chemicals include mineral spirits, mineral and true turpentine, acetone, naphtha, toluene, methyl ethyl ketone (MEK), dimethylformamide (DMF), glycol ethers and xylene.