flatten

American  

[flat-n] / ˈflæt n /

verb (used with object)

1. to make flat.

2. to knock down.

   The boxer flattened his opponent in the second round.

   Synonyms:

   floor, deck, prostrate, fell, ground

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verb (used without object)

1. to become flat.

verb phrase

1. flatten out to fly into a horizontal position, as after a dive.

2. flatten in flat.

flatten British  

/ ˈflætən /

verb

1. (sometimes foll by out) to make or become flat or flatter

2. informal (tr)

   1. to knock down or injure; prostrate

   2. to crush or subdue

      failure will flatten his self-esteem

3. Usual US word: flat.  (tr) music to lower the pitch of (a note) by one chromatic semitone

4. to manoeuvre an aircraft into horizontal flight, esp after a dive

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Other Word Forms

• flattener noun
• overflatten verb (used with object)
• unflattened adjective

Etymology

Origin of flatten

First recorded in 1620–30; flat ¹ + -en ¹

Explanation

When you flatten something, you crush it or level it out. If the recycling bin is getting full, you should probably flatten all those cans you're adding to it. You might flatten the batter in a cake pan before baking it, or flatten the grass along a path through a field. If your curly hair tends to get frizzy in humid weather, you may try to flatten it before you leave for school in the morning. You also might flatten yourself against a wall if you're hiding from your friend, or describe a terrible storm this way: "The tornado managed to flatten several buildings."

Example Sentences

Moderate relief is in sight this weekend, however, when forecasters predict the powerful high pressure system will start to flatten out, bringing a gradual drop in temperatures.

From Los Angeles Times • Mar. 19, 2026

“We’re just seeing this trend flatten out,” Berner said.

From MarketWatch • Mar. 12, 2026

The larger the organization, the tougher it is to flatten, keeping it slow, rigid and blind.

From The Wall Street Journal • Mar. 1, 2026

But that doesn’t necessarily flatten one more than the other.

From Salon • Feb. 26, 2026

My mother said she used a laundry iron to flatten it out before pasting it next to hers in the scrapbook.

From "Flush" by Carl Hiaasen

Related Words

• crush
• raze
• smash
• straighten