wall off vs washboard

wall off

verb
  • To separate with a wall. 

  • To isolate completely. 

washboard

verb
  • To move up and down or back and forth across the surface of a hive, possibly to lay down a layer of propolis and wax. 

  • To play a washboard. 

  • To produce a rippled texture on a surface. 

noun
  • A stretch of ripples or bumps on a dirt or gravel road caused by interaction between traffic and road surface. 

  • A board fastened along a ship's gunwale to prevent splashing; a splashboard. 

  • Such a board used as a simple percussion instrument. 

  • A board with a corrugated surface against which laundry may be rubbed. 

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