convention vs double date

convention

noun
  • The convening of a formal meeting. 

  • A formal agreement, contract, rule, or pact. 

  • A treaty or supplement to such. 

  • A meeting or gathering. 

  • A practice or procedure widely observed in a group, especially to facilitate social interaction; a custom. 

  • A formal deliberative assembly of mandated delegates. 

double date

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

verb
  • To go on a double date. 

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