Clear·ance n.
 1. The act of clearing; as, to make a thorough clearance.
 2. A certificate that a ship or vessel has been cleared at the customhouse; permission to sail.
    Every ship was subject to seizure for want of stamped clearances.   --Durke
 3. Clear or net profit.
 4. 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.
 Clearance space 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.
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