a zone in central Panama, crossing the Isthmus of Panama on both sides of the Panama Canal: governed by the U.S. from 1903 until 1979, when most of the zone was returned to Panama, for its eventual control of the entire zone by 2000; ab. 10 mi. (16 km) wide; excludes the cities of Panama and Colón. 44,650; 553 sq. mi. (1432 sq. km). Abbr.: CZ (for use with zip code), C. Z.