flatten

verb

1. (transitive)To make something flat or flatter.

   “As there was a lot of damage, we chose the heavy roller to flatten the pitch.”

   “Mary would flatten the dough before rolling it into pretzels.”

   “Attempting to block the police van's path, protesters periodically surrounded the vehicle and eventually flattened one of its tires.”

2. (reflexive)To press one's body tightly against a surface, such as a wall or floor, especially in order to avoid being seen or harmed.

   “With a bolt of fright he remembered that there was no bathroom in the Hob-house Room. He leapt along the corridor in a panic, stopping by the long-case clock at the end where he flattened himself against the wall.”

3. (transitive)To knock down or lay low.

   “The prize fighter quickly flattened his challenger.”

4. (intransitive)To become flat or flatter; to plateau.

   “Prices have flattened out.”

5. (intransitive)To be knocked down or laid low.
6. To lower by a semitone.
7. To make vapid or insipid; to render stale.
8. (transitive)To reduce (a data structure) to one that has fewer dimensions, e.g. a 2×2 array into a list of four elements.
9. (transitive)To combine (separate layers) into a single image.