flatten  
verb [ I or T ] uk/ˈflæt.ən/ us/ˈflæt̬.ən/
  (BECOME LEVEL)      
 C2 (使)变平,把…弄平
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。 
 - More examples
 - He was immediately flattened by a single punch to the head.
 - The whole area was flattened in the bombing raid - not a building was left standing.
 - After a few hundred yards, you come to an area where the ground flattens out.
 - That tent is not secure, you know. The first gust of wind will flatten it.
 - A fight broke out and we had to grab Kevin to stop him flattening the other guy.
 
  (MAKE THINNER)      
C2 (使)变平坦;(使)变薄
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。