sugar (or sweeten) the pill make an unpleasant or painful necessity more acceptable.
☞ The image here is of making bitter-tasting medicine more palatable by adding sugar.
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。