Rust
/rˈʌst/
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Definition
(noun) The deteriorated state of iron or steel as a result of moisture and oxidation; it consists mostly of iron(III) oxide (ferric oxide) and iron(II) oxide (ferrous oxide).
Sentence Examples
Too much rest is rust.
A bicycle will rust if you leave it in the rain.
CEFR Practice Quiz
The old bicycle had been left outside so long that ____ had spread across the frame.