life line vs lifeline

life line

lifeline

noun
  • A particular crease in the palm. 

  • A line from the diver to a tender at the surface control point. 

  • A line to which a drowning or falling victim may cling. 

  • A means or route for transporting indispensable supplies. 

  • System or structure of vital importance to a community. 

  • A source of salvation in a crisis. 

  • On the deck of a boat, a line to which one can attach oneself to stay aboard on rough seas. 

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