The only free and comprehensive online etymological dictionary of the Spanish language
kilo- (Prefix) "thousand"
19th cent. Borrowed from French kilo- 'id.,' itself borrowed from Ancient Greek χίλιοι ‎(khílioi) 'id.' From Proto-Indo-European *ghes-lo- "thousand," "a great number." The same root as mil.
Sanskrit sahásra- "thousand," Avestan hazaŋra- 'id.'
kilómetro m. (Noun) "kilometer"
19th cent. A thousand meters. From kilo- "thousand" and metro.