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

---

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

---

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, 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

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

Upstairs, Dad has me flatten a stack of empty boxes while he puts the books on the bookshelves.

From "Liar & Spy" by Rebecca Stead

Related Words

• crush
• raze
• smash
• straighten