noun
express dispatch; urgent correspondence
Refers to sending something quickly, often used in business or postal contexts. Can be a noun or used attributively.
この書類は急便で送ってください。
Please send these documents by express delivery.
急便の手紙が今朝届いた。
An urgent letter arrived this morning.
Compound of 急 (urgent) and 便 (mail, convenience). The exact historical derivation is uncertain, but the word is used in modern Japanese for express delivery services.