epitaph vs grave marker

epitaph

noun
  • An inscription on a gravestone in memory of the deceased. 

  • A poem or other short text written in memory of a deceased person. 

verb
  • To write or speak after the manner of an epitaph. 

  • To commemorate by an epitaph. 

grave marker

noun
  • A tombstone or other permanent fixed object to indicate the location of a grave. 

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