1
a
: the reddish brittle coating formed on iron especially when chemically attacked by moist air and composed essentially of hydrated ferric oxide
b
: a comparable coating produced on a metal other than iron by corrosion
c
: something resembling rust : accretion
2
: corrosive or injurious influence or effect
3
: any of numerous destructive diseases of plants produced by fungi (order Uredinales) and characterized by usually reddish-brown pustular lesions
also
: a fungus causing this
4
: a strong reddish brown
rusted; rusting; rusts
1
: to form rust : become oxidized
iron rusts
2
: to degenerate especially from inaction, lack of use, or passage of time
most men would … have allowed their faculties to rust—
T. B. Macaulay
T. B. Macaulay3
: to become reddish brown as if with rust
the leaves slowly rusted
4
: to be affected with a rust fungus
1
: to cause (a metal) to form rust
keep up your bright swords, for the dew will rust them—William Shakespeare
William Shakespeare2
: to impair or corrode by or as if by time, inactivity, or deleterious use
3
: to cause to become reddish brown : turn the color of rust
Examples of rust in a Sentence
Noun
an old pump covered in rust
Verb
Your bicycle will rust if you leave it out in the rain.
The moist air rusted the latch on the door.
The old iron fence was rusted.
Recent Examples on the Web
Tim Johnson, Chicago Tribune, 19 July 2025
For example, tan gravel complements an adobe wall, and rust red gravel contrasts with it.
—Luke Miller, Better Homes & Gardens, 17 July 2025
Susannah Bryan, Sun Sentinel, 17 July 2025
Hypoallergenic stainless steel ensures the pieces are gentle on skin and don’t rust, even with constant exposure to moisture or sweat.
—Kaitlyn Gomez, USA Today, 4 July 2025
See All Example Sentences for rust
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Noun
This is a telltale sign of rust (and is also very annoying).
—Tim Johnson, Chicago Tribune, 19 July 2025
For example, tan gravel complements an adobe wall, and rust red gravel contrasts with it.
—Luke Miller, Better Homes & Gardens, 17 July 2025
Verb
In addition, the metal mesh screening that supports the lights had already started rusting.
—Susannah Bryan, Sun Sentinel, 17 July 2025
Hypoallergenic stainless steel ensures the pieces are gentle on skin and don’t rust, even with constant exposure to moisture or sweat.
—Kaitlyn Gomez, USA Today, 4 July 2025
See All Example Sentences for rust
Cite this Entry
“Rust.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/rust. Accessed 26 Jul. 2025.
Copy CitationKids Definition
rust
1 of 2 noun1
: a reddish brittle coating formed on iron especially when chemically attacked by moist air and composed chiefly of ferric oxide
2
a
: any of numerous destructive diseases of plants caused by fungi and characterized by reddish brown spots
b
: any of an order of fungi that cause plant rusts
3
: a reddish brown
rust
2 of 2 verb
: to form or cause to form rust
iron rusts
Medical Definition
rust
noun1
: the reddish brittle coating formed on iron especially when chemically attacked by moist air and composed essentially of hydrated ferric oxide
2
: any of numerous destructive diseases of plants produced by fungi (order Uredinales) and characterized by reddish brown pustular lesions
also
: a fungus causing this
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