lop off
phrasal verblop something  off (something) 
- to remove part of something by cutting it, especially to remove branches from a tree砍掉;剪掉;修剪(树枝) 
- to make something smaller or less by a particular amount削减;减少 - They lopped 20p off the price.他们把价格降了 20 便士。 
 
- They lopped 20p off the price.