Definition of Lancaster
1a city in western England, north of Liverpool, on the estuary of the Lune River; population 44,500 (est. 2009). 2a city in southwestern California, northeast of Los Angeles, on the edge of the Mojave Desert; population 145,469 (est. 2008). 3a city in southeastern Pennsylvania, primarily a commercial center for the Pennsylvania Dutch Country; population 54,626 (est. 2008).