The Collaborative International Dictionary of English v.0.48:

Aluminum \A*lu"mi*num\ ([.a]*l[=u]*m[i^]*n[u^]m), n.
   The metallic element forming the base of alumina. This metal
   is white, but with a bluish tinge, and is remarkable for its
   resistance to oxidation, and for its lightness, having a
   specific gravity of about 2.6. Atomic weight 27.08. Symbol
   Al. Also called aluminium.
   [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

aluminum
    n 1: a silvery ductile metallic element found primarily in
         bauxite [syn: aluminum, aluminium, Al, atomic number
         13]

The Elements (07Nov00):

aluminum
Symbol: Al
Atomic number: 13
Atomic weight: 26.9815
Silvery-white lustrous metallic element of group 3 of the periodic
table.
Highly reactive but protected by a thin transparent layer of the oxide
which quickly forms in air. There are many alloys of aluminum, as well
as
a good number of industrial uses. Makes up 8.1% of the Earth's crust, by
weight. Isolated in 1825 by H.C. Oersted.