Lubricant (noun)

1. A substance, such as oil or grease, used to reduce friction and heat between two moving surfaces.
2. Something that makes things run smoothly.

Origin:

Late middle english (also in the sense "something that makes smooth or slippery"): from latin lubricant- "making slippery", from the verb lubricare.

Examples:

1. The engine needs lubricant to run smoothly.
2. He used lubricant to make it easier to insert the tube.
3. The lubricant reduced friction between the gears.
4. The lubricant made it easy to move the metal parts.
5. The lubricant was used to reduce the wear and tear on the machinery.