Meaning

noun a metric unit of length equal to 1000 meters (or 0.621371 miles)

origin* Most likely a pseudo-condensed pronunciation of kilometer, being a suitably short word emphasizing k+l instead of /keɪ/ alone (the same principle as with military spelling alphabets, but also clearly distinguished from kilo (/kiːloʊ/) for kilogram). * Possibly onomatopoeic of the sound of a military odometer. When a soldier would complete a mark, they would signal to their commander and denote…

Etymology from Wiktionary, CC BY-SA 3.0