clearance vs empty space

clearance

noun
  • The act of clearing or something (such as a space) cleared. 

  • The first disposal in a chain that leaves the area of a stoppage, or a disposal that leaves the area of a stoppage itself. 

  • A permission for a vehicle to proceed, or for a person to travel. 

  • A permission to have access to sensitive or secret documents or other information. 

  • The act of kicking a ball away from the goal one is defending. 

  • The act of potting all the remaining balls on a table at one visit. 

  • Clear or net profit. 

  • The settlement of transactions involving securities or means of payment such as checks by means of a clearing house. 

  • A permission to use something, usually intellectual property, that is legally, but not otherwise, protected. 

  • 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. 

  • The distance between two moving objects, especially between parts of a machine 

  • A sale of merchandise, especially at significantly reduced prices, usually in order to make room for new merchandise or updated versions of the same merchandise. 

  • The removal of harmful substances from the blood; renal clearance. 

  • Removal of pieces from a rank, file or diagonal so that a bishop, rook or queen is free to move along it. 

  • The act of leaving the area of a stoppage. 

empty space

noun
  • An unoccupied space where something may be stored 

  • Vacuum; a space containing nothing at all 

  • A feeling of longing for someone or something that is gone; a sense of a thing's absence. 

  • An unoccupied area or volume. 

How often have the words clearance and empty space occurred in a corpus of books? (source: Google Ngram Viewer )