clearance

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The act or process of clearing.
• noun A space cleared; a clearing.
• noun The amount of space or distance by which a moving object clears something.
• noun The height or width of a passage.
• noun An intervening space or distance allowing free play, as between machine parts.
• noun Permission for an aircraft, ship, or other vehicle to proceed, as after an inspection of equipment or cargo or during certain traffic conditions.
• noun Official certification of blamelessness, trustworthiness, or suitability.
• noun A sale, generally at reduced prices, to dispose of old merchandise.
• noun The passage of checks and other bills of exchange through a clearing-house.
• noun The removal by the kidneys of a substance from blood plasma.
• noun Renal clearance.

from The Century Dictionary.

• noun A piece of land which has been cleared for cultivation or for building; a clearing.
• noun In railroading: A difference between the track-gage and the gage of the exterior surface of the wheel-flanges, designed to allow a certain amount of play between the flanges and the rails.
• noun At a crossing or frog, the clear space left between cross-rails and the frog and guard-rail for the free passage of the flanges of the wheels.
• noun The clear space between the sides and top of a tunnel or bridge and the outside dimensions of the largest car passing through it.
• noun In steam-engines, the volume or entire space below the valve-face which is filled with steam at the beginning of a stroke, including the space between piston and cylinder-head and the volume of the steam-ducts to the valve-seat.
• noun The settlement or payment of a debt; the passing of checks and drafts through the clearing-house for their settlement.
• noun The act of clearing; riddance; removal of encumbrance or obstruction: as, the clearance of land from trees; the clearance of an estate from unprofitable tenantry.
• noun Clear or net profit.
• noun A certificate that a vessel has complied with the law and is authorized to leave port.
• noun In steam-engines, the distance between the piston and the cylinder-cover, when the former is at the end of its stroke; similarly, free play for the parts of any other machine; clearing.

from the GNU version of the Collaborative International Dictionary of English.

• noun The act of clearing.
• noun A certificate that a ship or vessel has been cleared at the customhouse; permission to sail.
• noun Clear or net profit.
• noun (Mach.) The distance by which one object clears another, as the distance between the piston and cylinder head at the end of a stroke in a steam engine, or the least distance between the point of a cogwheel tooth and the bottom of a space between teeth of a wheel with which it engages.
• noun (Steam engine) the space inclosed in one end of the cylinder, between the valve or valves and the piston, at the beginning of a stroke; waste room. It includes the space caused by the piston's clearance and the space in ports, passageways, etc. Its volume is often expressed as a certain proportion of the volume swept by the piston in a single stroke.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The act of clearing or something (such as a space) cleared
• noun The distance between two moving objects, especially between parts of a machine
• noun The height or width of a tunnel, bridge or other passage, or the distance between a vehicle and the walls or roof of such passage; a gap, headroom.
• noun A permission for a vehicle to proceed, or for a person to travel.
• noun A permission to have access to sensitive or secret documents or other information
• noun A sale of merchandise at a reduced price.
• noun banking, finance The settlement of transactions involving securities or means of payment such as checks by means of a clearing house.
• noun medicine The removal of harmful substances from the blood; renal clearance.
• noun sports, billiards, snooker, pool The act of potting all the remaining balls on a table at one visit.
• noun soccer The act of kicking a ball away from the goal one is defending.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the distance by which one thing clears another; the space between them
• noun permission to proceed
• noun vertical space available to allow easy passage under something