from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A colorless, odorless inert gaseous element occurring in natural gas and with radioactive ores. It is used as a component of artificial atmospheres and laser media, as a refrigerant, as a lifting gas for balloons, and as a superfluid in cryogenic research. Atomic number 2; atomic weight 4.0026; boiling point -268.9°C; density at 0°C 0.1785 gram per liter. See Table at element.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A colorless and inert gas, and the second lightest chemical element (symbol He) with an atomic number of 2 and atomic weight of 4.002602.
- n. A form or sample of the element.
from the GNU version of the Collaborative International Dictionary of English
- n. An inert, monoatomic, gaseous element occurring in the atmosphere of the sun and stars, and in small quantities in the earth's atmosphere, in several minerals and in certain mineral waters. It is obtained from natural gas in industrial quantities. Symbol, He; atomic number 2; at. wt., 4.0026 (C=12.011). Helium was first detected spectroscopically in the sun by Lockyer in 1868; it was first prepared by Ramsay in 1895. Helium has a density of 1.98 compared with hydrogen, and is more difficult to liquefy than the latter. Chemically, it is an inert noble gas, belonging to the argon group, and cannot be made to form compounds. The helium nucleus is the charged particle which constitutes alpha rays, and helium is therefore formed as a decomposition product of certain radioactive substances such as radium. The normal helium nucleus has two protons and two neutrons, but an isotope with only one neutron is also observed in atmospheric helium at an abundance of 0.013 %. Liquid helium has a boiling point of -268.9° C at atmospheric pressure, and is used for maintaining very low temperatures, both in laboratory experimentation and in commercial applications to maintain superconductivity in low-temperature superconducting devices. Gaseous helium at normal temperatures is used for buoyancy in blimps, dirigibles, and high-altitude balloons, and also for amusement in party balloons.
from The Century Dictionary and Cyclopedia
- n. A hypothetical elementary substance, known only by the lines ascribed to it in the solar spectrum.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. a very light colorless element that is one of the six inert gasses; the most difficult gas to liquefy; occurs in economically extractable amounts in certain natural gases (as those found in Texas and Kansas)
From Greek hēlios, sun (so called because its existence was deduced from the solar spectrum); see sāwel- in Indo-European roots.(American Heritage® Dictionary of the English Language, Fourth Edition)
From New Latin helium, from Ancient Greek ἥλιος (hēlios, "sun") (because its presence was first theorised in the sun's atmosphere). (Wiktionary)