The story
Partial calque of Japanese 軽自動車 (keijidōsha, literally “light car”).
Etymology from Wiktionary, CC BY-SA 4.0.
kei car
Today it means: A kind of light passenger automobile sold in Japan. Vehicles of this type are distinguished by the use of smaller engines (with displacement up to 660 cc), and yellow and black (or black and yellow) license plates. Full definition →