n. & v.
n. 1 a a reddish or yellowish-brown coating formed on iron or steel by oxidation, esp. as a result of moisture. b a similar coating on other metals. 2 a any of various plant-diseases with rust-coloured spots caused by fungi of the order Uredinales. b the fungus causing this. 3 an impaired state due to disuse or inactivity.
v. 1 tr. & intr. affect or be affected with rust; undergo oxidation. 2 intr. (of bracken etc.) become rust-coloured. 3 intr. (of a plant) be attacked by rust. 4 intr. lose quality or efficiency by disuse or inactivity. rustless adj.
[ OE rust f. Gmc ]