oiloil1 /ɔɪl/ ●●● noun 1 [uncountable] earth science a thick dark liquid from under the ground, from which gasoline and other products are made SYN petroleum: The price of oil is rising. The oil industry made huge profits this year.2[uncountable] a smooth thick liquid that is burned to produce heat or used for making machines run easily: We need to get the oil changed in the car.3[countable, uncountable] a smooth thick liquid made from plants or animals, used in cooking or for making beauty products: Fry the chicken in oil. Use a tablespoon of olive/sunflower/vegetable oil to cook the meat.4oils [plural] eng. lang. arts paints that contain oil [Origin: 1100–1200 Old French oile, from Latin oleum “olive oil”]