The Kostak surname is derived from the personal names Kosty and Kost, which are pet forms of the male given name Konstanty, which is the Polish form of the name Constantine. The name Constantine is a derivative of the Latin name Constantinus, which means steadfast and faithful. This name was borne by the first Christian ruler of the Roman Empire, Constantine the Great (280-337). Constantine rebuilt the city named Byzantium, renamed it Constantinople and made it the capital city of the Eastern Roman Empire. Constantinople is the modern city of Istanbul, Turkey.