gratuitygra·tu·i·ty /grəˈtjuːəti-ˈtuː-/ noun (plural gratuities) [countableC] formal1a small amount of money given to someone for a service they provideSYN TIPIn many restaurants, a small gratuity given in advance may greatly improve service.
2British EnglishBrEHUMAN RESOURCES a large amount of money given to someone when they leave their job, especially when they leave the army, navy etcHe received a gratuity of £11,000 when he left the services.