first-day cover

envelope with a set of special stamps postmarked on the first day of issue 首日封.

first balcony, first base, first class, first cousin, first degree, first finger, first floor, first gear, first lady, first name, first night, first of all, first offender, first officer, first or last, first refusal, first school, first-aid, first-born, first-class, first-footing, first-fruit, first-hand, first-rate, firsthand, firstly, firth, fiscal, fiscal year, fish, fish and chips, fish cake, fish finger (US fish stick), fish out, fish pond, fish weir, fish-eye lens, fish-farm, fish-hook, fish-kettle,