alveolate vs unfilled

alveolate

noun
  • A member of a grouping of protists comprising the ciliates, sporozoa and dinoflagellates. 

adj
  • Having a structure containing honeycomb-like cavities. 

unfilled

adj
  • Not filled, especially occupational positions. 

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