Definitions
1.VerbTo 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."
2.VerbTo press one's body tightly against a surface, such as a wall or floor, especially in order to avoid being seen or harmed.
3.VerbTo knock down or lay low."The prize fighter quickly flattened his challenger."
4.VerbTo become flat or flatter; to plateau."Prices have flattened out."
5.VerbTo be knocked down or laid low.
6.VerbTo lower by a semitone.
7.VerbTo make vapid or insipid; to render stale.
8.VerbTo reduce (a data structure) to one that has fewer dimensions, e.g. a 2×2 array into a list of four elements.
9.VerbTo combine (separate layers) into a single image.