cenotaph vs undercroft

cenotaph

noun
  • A monument, generally in the form of an empty tomb, erected to honour the dead whose bodies lie elsewhere, especially members of the armed forces who died in battle. 

undercroft

noun
  • A cellar or vaulted storage room. 

  • A ground-level car park that occupies the base of a building. 

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