1. To apply oil, grease, or other similar substances to engine components in machines, automobiles, etc. so they will slide smoothly and easily against each other: When something is lubricated, it reduces friction and wear on the connecting parts and so they do not wear out so quickly.

Sometimes a person needs to lubricate rusty bolts so they can be unscrewed.

Mechanics who work on cars usually need to lubricate certain engine parts in order to remove old ones and to attach new ones.

Different kinds of machines and engines, from jumbo jets to sewing machines, need to be lubricated in order for them to work properly.

Hyaluronic acid, a viscous slippery substance that lubricates the joints in the body, maintains the shape of the eyeballs, and is a key component of connective tissue, is inside the knees, elbows, fingers, etc. of people and it helps to lubricate and cushion the joints; in fact, hyaluronic acid is a lubricating substance found naturally in all of the joints of the body.

2. Etymology: from Latin lubricatum, "made slippery".