查词历史：
- first-class mail first tempering bin first surplus treaty first sugar first proof first past the post first moment of mass first mean value theorem first lady first electroviscous effect firmly firm firing temperature firing squad firing order fireworks firedoor handle firebox crosstie firearm
- Noun
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1. mail that includes letters and postcards and packages sealed against inspection
- synonym： first class，1st class，1st-class mail，priority mail
法律
- 1.第一类邮件
