deuterium
/djuːˈtɪərɪəm/noun
mass noun
- Chemistry a stable isotope of hydrogen with a mass approximately twice that of the usual isotope. (Symbol: D)【化】氘, 重氢（符号： D）。
Deuterium atoms have a neutron as well as a proton in the nucleus, and the isotope is present to about 1 part in 6, 000 in naturally occurring hydrogen. It is used as a fuel in thermonuclear bombs, and heavy water （D2O） is used as a moderator in nuclear reactors.
词源
1930s: modern Latin， from Greek deuteros 'second'.