- an inert, monatomic gaseous element, present in very small amounts in the atmosphere: used in high-power, tungsten-filament light bulbs. Symbol: Kr; atomic weight: 83.80; atomic number: 36.
- an inert gaseous element occurring in trace amounts in air and used in fluorescent lights and lasers. Symbol: Kr; atomic no: 36; atomic wt: 83.80; valency: 0; density: 3.733 kg/m³; melting pt: –157.37°C; boiling pt: –153.23±0.10°C
