on the back of an envelope used in reference to calculations or plans of the most sketchy kind.
2013Daily Telegraph This two-boat, dual use idea has been dreamt up at the last minute on the back of an envelope, with no financial analysis.
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。