Other forms: rusts
Rust is the flaking red-brown crust that eats away iron. Covered in rust, rust spots, the car has rusted.
It is worse than most corrosion because it flakes: the crust does not seal the metal underneath, so the process keeps going down. Aluminium and stainless steel form tight oxide layers instead and stop. Rust needs both oxygen and water, so dry iron does not rust.
1nounrustThe red-brown crust that forms on iron.
“The old bike was covered in rust after years out in the rain.”
2verbformOf iron or steel: to be slowly eaten away by a red-brown crust in damp air.
“Leave the bike out in the rain all winter and the chain will rust.”
Too few real examples of this word to estimate which sense is commonest.
Old English rust names the crust, from a Germanic root about redness. Red and russet are relatives.
Proto-Indo-European
*h₁rewdʰ-
Proto-Indo-European
*rudʰso- — red
Proto-Germanic
*rustaz — rust
Proto-West Germanic
*rust
Old English
rust
Middle English
rust
English, today
rust
Built from
From Middle English rust, rost, roust, from Old English rust, rūst (“rust”), from Proto-West Germanic rust, from Proto-Germanic rustaz (“rust”), from Proto-Indo-European rudʰso- (“red”), from Proto-Indo-European h₁rewdʰ- (“red”). Cognate with Scots roust (“rust”), stq rust (“rust”), West Frisian roast (“rust”), Dutch roest (“rust”), German Rost (“rust”), Danish rust (“rust”), Swedish rost (“rust”), Norwegian rust, ryst (“rust”), Finnish ruoste, Estonian rooste. Related to red.
Etymology from Wiktionary, CC BY-SA