motet vs psalm

motet

noun
  • A composition adapted to sacred words in the elaborate polyphonic church style; an anthem. 

psalm

noun
  • A sacred song; a poetical composition for use in the praise or worship of God. 

  • One of the hymns by David and others, collected into one book of the Old Testament, or a modern metrical version of such a hymn for public worship. 

verb
  • To extol in psalms; to make music; to sing 

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