If you flatten yourself against something, you press yourself flat against it, for example to avoid getting in the way or being seen. He flattened himself against a brick wall as I passed
To flatten something such as a building, town, or plant means to destroy it by knocking it down or crushing it. explosives capable of flattening a five-storey building. areas of flattened corn
If you flatten something or if it flattens, it becomes flat or flatter. He carefully flattened the wrappers and put them between the leaves of his book The dog's ears flattened slightly as Cook spoke his name. the pitiful shacks built of cardboard boxes, corrugated iron sheets and flattened oil drums. Flatten out means the same as flatten. The hills flattened out just south of the mountain Peel off the blackened skin, flatten the pepper out and trim it into edible pieces
If you flatten someone, you make them fall over by hitting them violently. `I've never seen a woman flatten someone like that,' said a crew member. `She knocked him out cold.'
lower the pitch of (musical notes) become flat or flatter; "The landscape flattened" make flat or flatter; "flatten a road"; "flatten your stomach with these exercises