(uncountable) The second lightest chemical element (symbol He) with an atomic number of 2 and atomic weight of 4.002602, a colorless, odorless and inert noble gas.

plural of helium

plural of helium star

plural of helium variable

(physics) The normal isotope of helium, ⁴₂He, that has two neutrons

(physics) The rare isotope of helium, ³₂He, that has a single neutron

Speech whose timbre (but not pitch) has been affected by the inhalation of helium, due to the difference in the speed of sound in that gas, compared with air.

(physics) The liquified form of helium that does not solidify even at absolute zero; it shows unusual properties, such as superfluidity, due to quantum effects.

(astronomy) The sudden beginning of the burning of helium in the core of stars of intermediate mass or on the surface of an accreting white dwarf.

(physics) nuclear fusion involving helium nuclei.