Where does “kilo-” come from?

kilo- (English) comes from French kilo-, 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.

kilo- (English): API; In the International System of Units and...