[ C/U ] thick, liquid fat obtained from plants which does not mix with water and is used esp. in cooking:

[ U ] a thick, liquid substance that burns and is used as fuel or as a lubricant (= substance that helps connecting parts move easily), or the thick liquid taken from under the ground which oil, gasoline, and other products are made from:

[ C ] any of a number of thick liquid substances that do not dissolve in water and are used in beauty products, paints, medicines, etc.

to add oil to something so it works better:

to put oil on a pan or other surface that you cook on to keep things from sticking to it:

NATURAL RESOURCES a thick liquid that comes from under the Earth's surface and is used as a fuel and for making plastics, etc.:

to put oil on something, especially a machine, to make it work more easily without sticking: