(archaeology) a method of determining the age of rock that depends on the production of helium during the decay of various radioactive isotopes of uranium and thorium.

(physics, astronomy) the nucleosynthesis process, in stars with temperatures over 10⁸K, in which helium is converted to carbon and then to oxygen, neon and magnesium

(astronomy) A star in which the strength of the helium absorption lines vary periodically; at times appearing to be a helium star.

(astronomy) A star which has lost most or all of its hydrogen, leaving just a core of helium.

(inorganic chemistry) Ellipsis of helium hydride cation. The unstable binary cation HeH⁺ present in interstellar space. It is the strongest acid, reactive with every chemical species except positive ions, including electrons.

(technical diving, saturation diving, underwater diving) Synonym of helium descrambler

(technical diving, saturation diving, underwater diving) An electronic device that lowers the pitch of speech, to compensate for the high-pitched speech of someone breathing in a helium atmosphere breathing mix (ie. heliox, heliair, ...), so as to be understandable to other people.

plural of helium flash

(physics) Having the electronic structure of a helium atom

Synonym of helide