dell vs empty space

dell

noun
  • A valley, especially in the form of a natural hollow, small and deep. 

empty space

noun
  • An unoccupied area or volume. 

  • Vacuum; a space containing nothing at all 

  • An unoccupied space where something may be stored 

  • A feeling of longing for someone or something that is gone; a sense of a thing's absence. 

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