seat belt vs tether

seat belt

noun
  • A restraining belt attached to a vehicle seat and fastened around occupants in order to keep them in place and decelerate them smoothly rather than suddenly in an accident, mitigating the risk of injury from uncontrolled impact with injurious objects. 

tether

noun
  • a rope, cable etc. that holds something in place whilst allowing some movement 

  • a strong rope or line that connects a sailor's safety harness to the boat's jackstay 

  • the limit of one's abilities, resources etc. 

  • The cardinal number three in an old counting system used in Teesdale and Swaledale. (Variant of tethera) 

verb
  • to connect something to something else. 

  • to connect a cellular smartphone to another personal computer in order to give it access to a hotspot. 

  • to restrict something with a tether. 

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