1. an oil that hardens in air due to oxidation and is often used as a paint or varnish base;
The Collaborative International Dictionary of English v.0.48:
Drying \Dry"ing\, a.
1. Adapted or tending to exhaust moisture; as, a drying wind
or day; a drying room.
2. Having the quality of rapidly becoming dry.
Drying oil, 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 (r) 3.0 (2006):
n 1: an oil that hardens in air due to oxidation and is often
used as a paint or varnish base