cookout vs gratin

cookout

noun
  • A gathering for a meal that is cooked and eaten outside; either a domestic barbecue or a larger social event. 

gratin

noun
  • The top crust of a dish, consisting of breadcrumbs or grated cheese heated under a grill; the dish itself. 

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