- clearance (n.)
[clearance 词源字典]
- 1560s, "action of clearing," from clear (v.) + -ance. Meaning "a clear space" is from 1788. Meaning "approval, permission" (especially to land or take off an aircraft) is from 1944, American English; national security sense recorded from 1948. Clearance sale attested by 1843.[clearance etymology, clearance origin, 英语词源]