citadel vs washboard

citadel

noun
  • An armoured portion of a warship, housing important equipment. 

  • A stronghold or fortified place. 

  • A Salvation Army meeting place. 

  • A strong fortress that sits high above a city. 

washboard

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

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

  • Such a board used as a simple percussion instrument. 

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

verb
  • To play a washboard. 

  • 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 produce a rippled texture on a surface. 

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