n :  a heavy colorless gas CO₂ that does not support combustion, dissolves in water to form carbonic acid, is formed esp. in animal respiration and in the decay or combustion of animal and vegetable matter, is absorbed from the air by plants in photosynthesis, and is used in the carbonation of beverages .
 
 
 
Published under license with Merriam-Webster, Incorporated.  © 1997-2024.