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

Example Sentences

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

From Los Angeles Times • Mar. 18, 2026

But she believes accent stereotypes can flatten a very rich linguistic landscape such as the one in Wales.

From BBC • Mar. 4, 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

When I find some I clean it off and flatten it out and store it between the pages of my school reader.

From "Cat's Eye" by Margaret Atwood

Related Words

• crush
• raze
• smash
• straighten