word-forming element meaning "one thousand," introduced in French 1795, when the metric system was officially adopted there; irregularly reduced from Greek khilioi "thousand," from PIE *gheslo- "thousand," source also of Sanskrit sahasra-, Avestan hazanjra "thousand." "It is usually assumed that Lat. mille should be connected too" [Beekes]; see milli-. "In the metric system, kilo- means multiplied, & milli- divided, by 1000" [Fowler].
liter n.
unit of capacity in the metric system, 1797, from French litre (1793), from litron, name of an obsolete French measure of capacity for grain (16c.), from Medieval Latin litra, from Greek litra "pound" (unit of weight), which apparently is from the same Sicilian Italic source as Latin libra (see Libra).
kilolitre n.
chiefly British English spelling of kiloliter; also see -re.