The term 'REWARD FOR WAITING' can be solved by two crossword solutions: TIPS (4 letters) and TIP (3 letters). TIPS is an acronym FOR 'To Insure Prompt Service' and is a gratuity given to service workers such as waiters, bellhops, and taxi drivers. TIP is an abbreviation FOR 'To Insure Promptness' and is a gratuity given to service workers in recognition of their prompt and courteous service. Both terms refer to the same concept of providing a REWARD FOR good service.