Rust/rʌst/ Definition 1 of 5Pro Tip 1/2Material Specific Use 'rust' for metals reacting with moisture, mainly iron and steel. The garden tools have started to rust after the rainy season. Pro Tip 2/2Visible Damage 'Rust' implies visible deterioration, often seen as an undesirable, damaging process. Check for any rust before buying the second-hand bike.