noun
Refers to the physical seal or seam of an envelope or similar closure. Often used in formal or written contexts.
See also: 緘する (かんする)
封筒の緘を切る。
I cut the seal of the envelope.
noun
writing on a seal
Specifically the characters or words written across the seal of an envelope, such as 〆 or 緘. Rare standalone use; more often encountered in compound or explanatory contexts.
封筒の緘の部分に「〆」と書く。
Write '〆' on the seal part of the envelope.