boundary vs middle

boundary

noun
  • The dividing line or location between two areas. 

  • An edge or line marking an edge of the playing field. 

  • The bounds, confines, or limits between immaterial things (such as one’s comfort zone, privacy, or professional sphere and the realm beyond). 

  • An event whereby the ball is struck and either touches or passes over a boundary (with or without bouncing), usually resulting in an award of 4 (four) or 6 (six) runs respectively for the batting team. 

  • (of a set) The set of points in the closure of a set S, not belonging to the interior of that set. 

middle

noun
  • A centre, midpoint. 

  • The part between the beginning and the end. 

  • The middle stump. 

  • The central part of a human body; the waist. 

  • The middle voice. 

adj
  • Pertaining to the middle voice. 

  • Located in the middle; in between. 

  • Central. 

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