rust

Concise Oxford English Dictionary © 2008 Oxford University Press:
rust/rʌst/

▶noun

• 1 a reddish- or yellowish-brown flaking coating of iron oxide that is formed on iron or steel by oxidation, especially in the presence of moisture.

• 2 a fungal disease of plants which results in reddish or brownish patches.

• 3 a reddish-brown colour.

▶verb be affected with rust.

– derivatives
rustless adjective.

– origin OE rūst, of Gmc origin; rel. to red.