life buoy vs lifeguard

life buoy

noun
  • Something that rescues one from difficulties. 

  • A buoyant object (most commonly torus-shaped) that is used as a life-saving device by keeping a person afloat. 

lifeguard

noun
  • A lifesaver. 

  • An attendant, usually an expert swimmer, employed to save swimmers in trouble or near drowning at a body of water. 

  • A sturdy metal bracket fixed in front of each of the leading wheels of a train to deflect small objects away from the wheels to prevent derailment. 

  • A bodyguard or unit of bodyguards, a guard of someone's (especially a king's) life or person. 

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