光こう速そく度どこうそくどMeanings1nounspeed of lightScientific term for the constant speed of light in a vacuum, approximately 3.0×10⁸ m/s. Also used in general contexts.光こう速そく度どは秒びょう速そく約やく30万まんキロメートルです。The speed of light is about 300,000 kilometers per second.
