elegy vs threnode

elegy

noun
  • A mournful or plaintive poem; a funeral song; a poem of lamentation. 

  • A composition of mournful character. 

  • A classical poem written in elegiac meter 

threnode

noun
  • A threne, or threnody; a dirge; a funeral song. 

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