Cs (Noun) — A soft silver-white ductile metallic element (liquid at normal temperatures); the most electropositive and alkaline metal.
Cs (Noun) — The speed at which light travels in a vacuum; the constancy and universality of the speed of light is recognized by defining it to be exactly 299,792,458 meters per second.
Cs (Noun) — The 3rd letter of the Roman alphabet.