Source : Webster's Revised Unabridged Dictionary (1913)

Helium \He"li*um\ (h[=e]"l[i^]*[u^]m), n. [NL., fr. Gr. "h`lios
   the sun.] (Chem.)
   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. Symbol, He; at. wt., 4. 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 belongs to the argon group
   and cannot be made to form compounds. It is a decomposition
   product of the radium emanation.

Helium \He"li*um\, n. [NL., fr. Gr. ? the sun.] (Chem.)
   A gaseous element found in the atmospheres of the sun and
   earth and in some rare minerals.

Source : WordNet®

helium
     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) [syn: {He}, {atomic
         number 2}]