ace in the hole vs mattress

ace in the hole

noun
  • Synonym of ace up one's sleeve 

mattress

verb
  • To cover with a thick layer, like a mattress; to blanket. 

noun
  • A pad on which a person can recline and sleep, usually having an inner section of coiled springs covered with foam or other cushioning material then enclosed with cloth fabric. 

  • A form of retaining wall used to support foundations or an embankment 

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