[clear.ance] n (1540) 1: an act or process of clearing: as a: the removal of buildings from an area (as a city slum) b: the act of clearing a ship at the customhouse; also: the papers showing that a ship has cleared c: the offsetting of checks and other claims among banks through a clearinghouse d: certification as clear of objection: authorization "security ~" e: a sale to clear out stock f: authorization for an aircraft to proceed esp. with a specified action "~ to land"
2: the distance by which one object clears another or the clear space between them
3: the volume of blood or plasma that could be freed of a specified constituent in a specified time (usu. one minute) by its excretion into the urine through the kidneys--called also renal clearance