FLATTEN

flatten, drop

(verb) lower the pitch of (musical notes)

flatten, flatten out

(verb) become flat or flatter; “The landscape flattened”

flatten

(verb) make flat or flatter; “flatten a road”; “flatten your stomach with these exercises”

Source: WordNet® 3.1

Etymology

Verb

flatten (third-person singular simple present flattens, present participle flattening, simple past and past participle flattened)

(transitive) To make something flat or flatter.

(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.

(transitive) To knock down or lay low.

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

(intransitive) To be knocked down or laid low.

(music) To lower by a semitone.

To make vapid or insipid; to render stale.

(programming, transitive) To reduce (a data structure) to one that has fewer dimensions, e.g. a 2×2 array into a list of four elements.

(computer graphics, transitive) To combine (separate layers) into a single image.

Source: Wiktionary

Flat"ten, v. t. [imp. & p. p. Flattened; p. pr. & vb. n. Flattening.] Etym: [From Flat, a.]

1. To reduce to an even surface or one approaching evenness; to make flat; to level; to make plane.

2. To throw down; to bring to the ground; to prostrate; hence, to depress; to deject; to dispirit.

3. To make vapid or insipid; to render stale.

4. (Mus.)

Definition: To lower the pitch of; to cause to sound less sharp; to let fall from the pitch. To flatten a sail (Naut.), to set it more nearly fore-and-aft of the vessel.

– Flattening oven, in glass making, a heated chamber in which split glass cylinders are flattened for window glass.

Flat"ten, v. i.

Definition: To become or grow flat, even, depressed dull, vapid, spiritless, or depressed below pitch.

Source: Webster’s Unabridged Dictionary 1913 Edition