drying oil

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. An organic oil, such as linseed oil, used as a binder in paints and varnishes. It dries into a tough elastic layer when applied in a thin film and exposed to air.

Wiktionary

1. n. An oil that hardens to a tough, solid film after a period of exposure to air.

GNU Webster's 1913

1. adj. an oil which, either naturally or after boiling with oxide of lead, absorbs oxygen from the air and dries up rapidly. Drying oils are used as the bases of many paints and varnishes.

WordNet 3.0

1. n. an oil that hardens in air due to oxidation and is often used as a paint or varnish base