jet bridge vs threshold

jet bridge

noun
  • An elevated corridor connecting an airport to a plane, usually enclosed and used for disembarking and embarking passengers and crew. 

threshold

noun
  • The start of the landing area of a runway. 

  • The outset of something; the point of entry, or the beginning of an action. 

  • The bottom-most part of a doorway that one crosses to enter; a sill. 

  • The point where one mentally or physically is vulnerable in response to provocation or to particular things in general. As in emotions, stress, or pain. 

  • An entrance; the door or gate of a house. 

  • The quantitative point at which an action is triggered, especially a lower limit. 

  • Any end or boundary. 

  • The wage or salary at which income tax becomes due. 

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