lum vs stairwell

lum

noun
  • A ventilating chimney over the shaft of a mine. 

  • A chimney; also, the top part of a chimney. 

  • A deep pool, especially one in a riverbed. 

  • A grove or wood; also, a woody valley. 

stairwell

noun
  • A shaft in a multi-story building enclosing a stairway or staircase. 

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