Yes, rust 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

Adjective

1. Of the brown color of rust

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