Where does “chiliarchus” come from?

chiliarchus (Latin) comes from Ancient Greek χιλίαρχος, from Ancient Greek χίλιοι, from Proto-Hellenic *kʰehliyoi, from Proto-Indo-European ǵʰéslom, from Proto-Indo-European sm̥-, from Proto-Indo-European sem- — together, one.

chiliarchus (Latin): chiliarch, commander of a thousand men in Ancient Greece