mule vs slipper

mule

noun
  • A shoe that has no fitting or strap around the heel, but which covers the foot. 

  • The generally sterile male or female hybrid offspring of a male donkey and a female horse. 

  • A coin or medal minted with obverse and reverse designs not normally seen on the same piece, either intentionally or in error. 

  • Any of a group of cocktails involving ginger ale or ginger beer, citrus juice, and various liquors. 

  • The generally sterile hybrid offspring of any two species of animals. 

  • A kind of triangular sail for a yacht. 

  • A stubborn person. 

  • A kind of cotton-spinning machine. 

  • A MMORPG character, or NPC companion in a tabletop RPG, used mainly to store extra inventory for the owner's primary character. 

  • A person paid to smuggle drugs. 

verb
  • To smuggle (illegal drugs). 

slipper

noun
  • A low soft shoe that can be slipped on and off easily. 

  • The plimsoll or gym shoe used in this form of punishment. 

  • A kind of bedpan urinal shaped like a shoe. 

  • A kind of brake or shoe for a wagon wheel. 

  • A person who slips. 

  • A piece, usually a plate, applied to a sliding piece, to receive wear and permit adjustment; a gib. 

  • A kind of apron or pinafore for children. 

  • A form of corporal punishment where the buttocks are repeatedly struck with a plimsoll; "the slipper". 

  • Such a shoe intended for indoor use; a bedroom or house slipper. 

  • A flip-flop (type of rubber sandal). 

verb
  • To spank with a plimsoll as corporal punishment. 

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