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helium

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he⋅li⋅um

[hee-lee-uhm]
–noun
an inert, gaseous element present in the sun's atmosphere and in natural gas, and also occurring as a radioactive decomposition product, used as a substitute for flammable gases in dirigible balloons. Symbol: He; atomic weight: 4.0026; atomic number: 2; density: 0.1785 g/l at 0°C and 760 mm pressure.

Origin:
1875–80; < NL < Gk hli(os) the sun + NL -ium -ium

helium I

–noun
colorless liquid helium existing below its boiling point of 4.2 K and above the lambda point of 2.186 K.

helium II

–noun
liquid helium existing as a superfluid below the lambda point of 2.186 K, having very low viscosity and very high thermal conductivity.
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2009.
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he·li·um   (hē'lē-əm)   
n.   Symbol He
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 Greek hēlios, sun (so called because its existence was deduced from the solar spectrum); see sāwel- in Indo-European roots.]
The American Heritage® Dictionary of the English Language, Fourth Edition
Copyright © 2009 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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Cultural Dictionary

helium

A chemical element, usually found in the form of a gas, in which two electrons are in orbit, and the nucleus consists of two protons and two neutrons. Its symbol is He.

Note: Helium is the best known of the inert gases.
Note: Because it is lighter than air, helium is used to fill balloons.
The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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Word Origin & History

helium 
1868, coined from Gk. helios "sun" (see sol), because the element was observed in the solar spectrum during the eclipse of Aug. 18, 1868, by Eng. astronomer Sir Joseph N. Lockyer (1836-1920) and Eng. chemist Sir Edward Frankland (1825-99). It was not actually obtained until 1895.
Online Etymology Dictionary, © 2001 Douglas Harper
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Medical Dictionary

Main Entry: he·li·um
Pronunciation: 'hE-lE-&m
Function: noun
: a light colorless nonflammable gaseous element found especially in naturalgases and used chiefly for inflating airships and balloons, for filling incandescent lamps, and for cryogenic research —symbol He; —see ELEMENT table
Merriam-Webster's Medical Dictionary, © 2002 Merriam-Webster, Inc.
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Medical Dictionary

helium he·li·um (hē'lē-əm)
n.
Symbol He
An inert gaseous element occurring in natural gas and used as a component of artificial atmospheres and laser media. Atomic number 2; atomic weight 4.0026; boiling point -268.9°C; density at 0°C 0.1785 gram per liter.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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