icicle vs stalactite

icicle

noun
  • A drooping, tapering shape of ice. 

stalactite

noun
  • A secondary mineral deposit of calcium carbonate or another mineral, in shapes similar to icicles, that hangs from the roof of a cave. 

  • Coordinate term: stalagmite 

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