Where does “Lancaster” come from?

Lancaster comes from Middle English Lancaster, derived from the Old English personal name Lancastre, which combined the River Lune with the Old English ceaster meaning "fort" or "Roman settlement."

Lancaster (English): The House of Lancaster, a dynasty of English kings and one of the opposing factions involved in the 15th century Wars of the Roses. The name comes from the fact that its members were descended from John of Gaunt, 1st Duke of Lancaster; their symbol was a red rose