boundary vs flank

boundary

noun
  • 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). 

  • The dividing line or location between two areas. 

  • 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. 

flank

noun
  • The wing, one side of the pitch. 

  • The flesh between the last rib and the hip; the side. 

  • The sides of a bastion perpendicular to the wall from which the bastion projects. 

  • The outermost strip of a road. 

  • That part of the acting surface of a gear wheel tooth that lies within the pitch line. 

  • A cut of meat from the flank of an animal. 

  • The side of something, in general senses. 

  • The extreme left or right edge of a military formation, army etc. 

verb
  • To be placed to the side(s) of something (usually in terms of two objects, one on each side). 

  • To defend the flank(s) of. 

  • To attack the flank(s) of. 

  • To place to the side(s) of. 

adj
  • Maximum. Historically faster than full speed (the most a vessel can sustain without excessive engine wear or risk of damage), now frequently used interchangeably. Typically used in an emergency or during an attack. 

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