Blacken on the grill is a cooking technique used to create a flavorful and charred crust on food. It involves heating the food over direct heat, usually on a grill, until it is blackened. The two crossword solutions for this term are 'SEAR' and 'CHAR'. To SEAR means to cook quickly over high heat, while charring is a longer process that involves cooking over lower heat for a longer period of time. Both techniques are used to create a flavorful and charred crust on food.