Oil  —n. 1 any of various viscous, usu. Inflammable liquids insoluble in water (cooking oil; drill for oil). 2 petroleum. 3 (in comb.) Using oil as fuel (oil-heater). 4 a (usu. In pl.) = *oil-paint. B picture painted in oil-paints. —v. 1 apply oil to; lubricate. 2 impregnate or treat with oil (oiled silk).  oil the wheels help make things go smoothly. [latin oleum olive oil]