Noun

1. The act of clearing or something (such as a space) cleared
2. The distance between two moving objects, especially between parts of a machine
3. 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.
4. A permission for a vehicle to proceed, or for a person to travel.

   The plane got clearance from air traffic control, and we were off.

   He got clearance to travel to America, even though he had previous links to terrorists

5. A permission to have access to sensitive or secret documents or other information
6. A sale of merchandise at a reduced price.
7. The settlement of transactions involving securities or means of payment such as checks by means of a clearing house.
8. The removal of harmful substances from the blood; renal clearance.
9. The act of potting all the remaining balls on a table at one visit.