Jacek is a Polish given name of Greek origin coming from Hyacinth, through the archaic form of Jacenty. Its closely related equivalents are: Jacinto (Spanish and Portuguese), Giacinto (Italian) and Jácint (Hungarian). There are some existing translations of "Jacek" into other languages, for instance the French Jacques, or English Jack, which are in fact the diminutive forms of such names as Jacob and John.
Read more about Jacek: Hyakinthos Myth