\Clear"ance\ (-ans), 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. --Trollope.
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.