flatten

UK: /ˈflæt^ən/ US: /ˈflætən/ ,(flat′n)

WordReference Random House Learner's Dictionary of American English © 2026

flat•ten /ˈflætən/   v. 

1. to (cause to) become flat: [~ (+ out) + object]
   Flatten (out) the pizza dough with your hands.
   [~ (+ out)]
   They flattened (out) against the wall and strained to see who was coming.
2. to knock down:
   [~ + object] The bulldozer flattened the barn.

WordReference Random House Unabridged Dictionary of American English © 2026

flat•ten  (flat′n), v.t. 

1. to make flat.
2. to knock down:
   The boxer flattened his opponent in the second round.

v.i. 

3. to become flat.
4. Nautical, Naval Terms flatten in, See flat ¹ (def. 57).
5. Aeronautics flatten out, to fly into a horizontal position, as after a dive.

• flat¹ + -en¹ 1620–30

flat′ten•er, n. 
Synonyms

• 2. . ground, fell, prostrate, deck, floor.

Collins Concise English Dictionary © HarperCollins Publishers::

flatten / ˈflæt^ən/ verb

1. (sometimes followed by out) to make or become flat or flatter
2. (transitive) to knock down or injure; prostrate
3. to crush or subdue
4. (transitive) to lower the pitch of (a note) by one chromatic semitone

ˈflattener noun