carbon dioxide UK /ˌkɑː.bən daɪˈɒk.saɪd/US /ˌkɑɹ.bən daɪˈɑk.saɪd/ noun1 •The normal oxide of carbon, CO₂; a colorless, odorless gas formed during respiration and combustion and consumed by plants during photosynthesis.There were dozens of presentations in 2008, including: [… — 2008