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a city in Yugoslavia, in the Socialist Republic of Croatia. Population, 38,000 (1971). Located on the Sava River at the influx of the Kupa River, Sisak is the uppermost point on the Sava that can be reached by navigation. In terms of freight turnover, it is the third busiest river port in Yugoslavia, after Belgrade and Novi Sad. The city is also a railroad junction. Sisak has a metallurgical industry, which includes the production of seamless tubing, and the chemical, electrical engineering, glass, woodworking, and food industries. It also has petroleum-refining and timber-chemistry enterprises.