The act of removing things to create space, or the amount of space between two objects. It can also mean official permission to do something, like see secret information or fly a plane.
From "clear" plus the noun-forming suffix "-ance." It keeps the sense of making something clear or free, whether of objects or of restrictions.
A "clearance sale" frees a store of stuff; security clearance frees you to enter secret zones. Same root idea: something blocking the way—objects or rules—gets pushed aside so you can move.
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