laugh up your sleeve be secretly or inwardly amused.
☞ The use of up in this expression is a relatively recent development; the phrase dates from the mid 16th century in the form laugh in your sleeve.
英语词组固定搭配大全包含15956条英汉双解词组，基本涵盖了全部常用英文词组、短语的翻译及用法，是英语学习的有利工具。