double date vs get together

double date

verb
  • To go on a double date. 

noun
  • A (romantic) date that two couples go on together. 

get together

verb
  • To start dating; to start being a couple. 

  • to agree 

  • to accumulate, to gather 

  • to meet, to gather together, to congregate 

  • Used other than figuratively or idiomatically: see get, together. 

How often have the words double date and get together occurred in a corpus of books? (source: Google Ngram Viewer )