函: 名词1.[书面语] (匣; 封套) case; envelope 短语和例子镜函 a case for a mirror2.(信件) letter 短语和例子公函 official letter; 函复 reply by letter; write a letter in reply; 函告 inform by letter; 来函 incoming letters; 索赔
保函: guarantee letterloi letter of indemnityl/g,letter of guarantee