- Noun. (inorganic compound) The normal oxide of carbon, CO2; a colorless, odorless gas formed during respiration and combustion and consumed by plants during photosynthesis.
- Noun. Compared to carbon monoxide, CO2 is a non-toxic gas, similar to the inert gases. Carbon dioxide is used on welding and lasers; unlike noble gases, it only reacts on water and minerals to produce carbonates and carbonic acid (chiefly referred as carbonation).