D₂O

Symbol

 * 1) A molecule of heavy water, comprising two deuterium atoms and an oxygen atom.
 * 2)  heavy water

Usage notes
IUPAC recommends that deuterium should be called by the chemical symbol "$2$H", not "D". It follows that heavy water should be called "$2$H$2$O", not "D$2$O".

Related terms

 * H₂O, light water
 * DHO, semi-heavy water