Yes, rusts is a Scrabble word!

Verb

1. Become destroyed by water, air, or a corrosive such as an acid

2. Cause to deteriorate due to the action of water, air, or an acid

3. Become coated with oxide

Noun

1. A red or brown oxide coating on iron or steel caused by the action of oxygen and moisture

2. A plant disease that produces a reddish-brown discoloration of leaves and stems; caused by various rust fungi

3. The formation of reddish-brown ferric oxides on iron by low-temperature oxidation in the presence of water

4. Any of various fungi causing rust disease in plants