The term 'Sooner Stater' is a nickname for a resident of the U.S. state of Oklahoma, which is commonly referred to as the 'Okie State'. The crossword solution for this term is 'OKIE', which is a four-letter word. This nickname is derived from the fact that settlers of the state were known as 'Sooners' because they arrived in the area before the official opening of the Unassigned Lands in 1889.