couple vs duad

couple

noun
  • A couple-close. 

  • A small number. 

  • That which joins or links two things together; a bond or tie; a coupler. 

  • Two partners in a romantic or sexual relationship. 

  • One of the pairs of plates of two metals which compose a voltaic battery, called a voltaic couple or galvanic couple. 

  • Two of the same kind connected or considered together. 

  • A turning effect created by forces that sum to zero in magnitude but produce a non-zero external torque. 

verb
  • To cause (two animals) to copulate, to bring (two animals) together for mating. 

  • To join in sexual intercourse; to copulate. 

  • To join (two things) together, or (one thing) to (another). 

det
  • Two or a few, a small number of. 

adj
  • Two or (a) small number of. 

duad

noun
  • A pair or couple. 

  • Dwadasama. 

  • An unordered pair. 

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