multitudes vs myriad

multitudes

noun
  • The mass of ordinary people; the populous or the masses. 

myriad

noun
  • A countless number or multitude (of specified things) 

  • Ten thousand; 10,000 

adj
  • Great in number; innumerable, multitudinous 

  • Multifaceted, having innumerable elements 

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