rust

American  

[ruhst] / rʌst /

noun

1. Also called iron rust.  the red or orange coating that forms on the surface of iron when exposed to air and moisture, consisting chiefly of ferric hydroxide and ferric oxide formed by oxidation.

2. any film or coating on metal caused by oxidation.

   Synonyms:

   corrosion

3. a stain resembling this coating.

4. any growth, habit, influence, or agency tending to injure, deteriorate, or impair the mind, character, abilities, usefulness, etc.

5. Plant Pathology.

   1. any of several diseases of plants, characterized by reddish, brownish, or black pustules on the leaves, stems, etc., caused by fungi of the order Uredinales.

   2. Also called rust fungus.  a fungus causing this disease.

   3. any of several other diseases of unknown cause, characterized by reddish-brown spots or discolorations on the affected parts.

6. reddish yellow, reddish brown, or yellowish red.

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verb (used without object)

1. to become or grow rusty, as iron.

2. to contract rust.

3. to deteriorate or become impaired, as through inaction or disuse.

   Synonyms:

   decline, decay

4. to become rust-colored.

verb (used with object)

1. to affect with rust.

2. to impair as if with rust.

3. to make rust-colored.

adjective

1. having the color rust.

verb phrase

1. rust out (of metal pipes, machinery, etc.) to decay and become unusable through the action of rust.

2. rust together to join two metal pieces, as iron pipes, by causing the joint to rust.

3. rust through to develop holes, breaks, or the like, because of rust.

rust British  

/ rʌst /

noun

1. a reddish-brown oxide coating formed on iron or steel by the action of oxygen and moisture

2. Also called: rust fungus.  plant pathol

   1. any basidiomycetous fungus of the order Uredinales , parasitic on cereal plants, conifers, etc

   2. any of various plant diseases characterized by reddish-brown discoloration of the leaves and stem, esp that caused by the rust fungi

3. 1. a strong brown colour, sometimes with a reddish or yellowish tinge

   2. ( as adjective )

      a rust carpet

4. any corrosive or debilitating influence, esp lack of use

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verb

1. to become or cause to become coated with a layer of rust

2. to deteriorate or cause to deteriorate through some debilitating influence or lack of use

   he allowed his talent to rust over the years

rust Scientific  

/ rŭst /

1. Any of the various reddish-brown oxides of iron that form on iron and many of its alloys when they are exposed to oxygen in the presence of moisture.

2. 1. Any of various basidiomycete fungi that are parasitic on plants and produce reddish or brownish spots on leaves. Rusts attack a wide variety of plants and can cause enormous damage to crops.

   2. Any of the various plant diseases caused by these fungi.

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1. To become corroded or oxidized.

Other Word Forms

• derust verb (used with object)
• rustless adjective
• unrust verb (used with object)

Etymology

Origin of rust

before 900; (noun) Middle English; Old English rūst; cognate with German Rost; (v.) Middle English rusten, derivative of the noun; akin to red ¹

Explanation

Rust is the reddish-brown stuff that forms over time on metal that's gotten wet. Your dad's beat-up old car probably has some rust on it somewhere. If you leave your bike out overnight in the rain, it'll be fine — you can dry it off the next day. If you leave it out for several rainy weeks, though, your bike will end up with rust on it. Rust appears as brown spots where the combination of water and oxygen has coated the metal with a compound that chemists call an oxide. Rust, which is also a verb, comes from a Germanic root meaning "redness."

Example Sentences

Since then, no maintenance has been undertaken, which means siren towers have been left to rust, while some have even had their batteries stolen, according to locals.

From BBC • Apr. 24, 2026

But O'Sullivan quickly shook off any "rust" as he moved into a controlling position and it would be a huge shock if He was able to fight back.

From BBC • Apr. 21, 2026

Some areas looked pixelated on the Chromebook, and on the Air I noticed details, like the leaves of a fern or rust on an airlock door, that weren’t as clear on the others.

From The Wall Street Journal • Mar. 14, 2026

"It's a long shot and ambitious but the species needs time and space without being constantly walloped by myrtle rust to hopefully express some resistance," Professor Fensham said.

From Science Daily • Mar. 13, 2026

Many of the greenhouse's windows had been shattered, and its iron frame was spotted with rust.

From "City of the Plague God" by Sarwat Chadda

Related Words

• decay
• deteriorate
• wither