Definition of "rust"

rust¹

/ɹʌst/

noun
countable and uncountable, plural rusts
1. The deteriorated state of iron or steel as a result of moisture and oxidation.
2. A similar substance based on another metal.
3. (color) A reddish-brown color.
4. A disease of plants caused by a reddish-brown fungus.
5. (philately) Damage caused to stamps and album pages by a fungal infection.

rust²

/ɹʌst/

verb
third-person singular simple present rusts, present participle rusting, simple past and past participle rusted
1. (intransitive) To oxidize, especially of iron or steel.
  Quotations
  Your gold and silver have rusted, and their rust will be evidence against you and will eat your flesh like fire.
  1946, International Council of Religious Education, The New Covenant, Commonly Called the New Testament of Our Lord and Savior Jesus Christ: Revised Standard Version, James 5:3, page 490
2. (transitive) To cause to oxidize.
3. (intransitive) To be affected with the parasitic fungus called rust.
  Quotations
  I am sorry to say that, contrary to the majority, I have to report that the forage rusted rather badly.
  1902 January 3, “Mapstone Oats: Further Experiences”, in The Agricultural Journal and Mining Record‎, volume 4, number 22, page 688
4. (transitive, intransitive, figuratively) To (cause to) degenerate in idleness; to make or become dull or impaired by inaction.
  Quotations
  Must I rust in Egypt? never more / Appear in arms, and be the chief of Greece?
  1692, John Dryden, Cleomenes, the Spartan Hero, a Tragedy
5. (intransitive) Of a black cat or its fur, to turn rust-coloured following long periods of exposure to sunlight.