bollard vs tether

bollard

noun
  • A strong vertical post of timber or iron, fixed to the ground and/or on the deck of a ship, to which the ship's mooring lines etc are secured. 

  • A similar post preventing vehicle access to a pedestrian area, to delineate traffic lanes, or used for security purposes. 

tether

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

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

  • 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 bollard and tether occurred in a corpus of books? (source: Google Ngram Viewer )