first day cover

Noun

(philately) A letter or card with new stamp, posted on the day that the stamp was first issued.

Japanese Meaning

初封筒：新しい切手が貼付され、切手が初めて発行された日に投函された手紙やカード

She carefully placed the first day cover into a protective sleeve before adding it to her album.

彼女は発行初日に消印された新しい切手の付いた封筒（初日カバー）を保護スリーブに慎重に入れてからアルバムに加えた。

Sense（1）

(philately) A letter or card with new stamp, posted on the day that the stamp was first issued.

first day covers

（ plural ）