The GEOnet Names Server (GNS) provides access to the National Geospatial-Intelligence Agency's (NGA) and the U.S. Board on Geographic Names' (US BGN) database of foreign geographic feature names. The GNS contains 4.0 million features with 5.5 million names - see
http://earth-info.nga.mil/gns/html/index.html

GEOnet Names Server (GNS)