What is "heavy water"

n. (context chemistry English) water containing deuterium instead of normal hydrogen (symbol D₂O); used as a moderator in nuclear reactors.

n. water containing a substantial proportion of deuterium atoms, used in nuclear reactors [syn: deuterium oxide]

Heavy water (deuterium oxide ( )) is a form of water that contains a larger than normal amount of the hydrogen isotope deuterium ( or D, also known as heavy hydrogen), rather than the common hydrogen-1 isotope ( or H, also called protium) that makes up most of the hydrogen in normal water.