to become level or cause something to become level

Several trees were flattened (= knocked down) by the storm. 暴风雨把几棵大树刮倒了。

The path flattens (out) (= does not go up so much) as it reaches the top of the hill. 到达山顶时，这条小路变得平坦了。

to become level and thinner or to cause something to become level and thinner

Flatten the pastry into a thin disc with your hands. 用手把油酥面团压成薄圆片。

The biscuits will flatten out as they cook. 烘烤时饼干会变得扁平。