double date vs have a thing

double date

verb

  • To go on a double date. 

noun

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

have a thing

verb

  • To be in a casual romantic relationship. 

  • To have a crush on, or a soft spot for, someone. 

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