light water

Alternative forms

 * lightwater
 * light-water

Noun

 * 1)  Water in its standard form of H$2$O, containing two protium ($1$H) hydrogen atoms, as opposed to heavy water (which contains deuterium, $2$H). (Natural water contains some deuterium, but not much; so it can safely be called light water.)
 * 2) Foam formed by water and a fluorocarbon surfactant, used in firefighting because it floats on flammable liquids lighter than water.

Synonyms

 * 1H2O

Hypernyms

 * H2O