When something is flattened, it becomes flat and less thick.
You might hear about things being flattened when they get squished or crushed. This can happen to objects like cars after an accident, or even to buildings during a strong earthquake. Sometimes people intentionally flatten things, like cardboard boxes for recycling, to make them easier to store or transport. If you try to squeeze a bunch of clothes into a small suitcase, you might end up with a flattened sweater that's no longer its original shape.
To make something flat or flatter.
Example: As there was a lot of damage, we chose the heavy roller to flatten the pitch.
Made flat by something.
Example: We removed the fallen tree from the flattened car.
