a·lu·mi·num (?-lo?o?m?-n?m)n. Symbol Al A silvery-white, ductile metallic element, the most abundant in the earth’s crust but found only in combination, chiefly in bauxite. Having good conductive and thermal properties, it is used to form many hard, light, corrosion-resistant alloys. Atomic number 13; atomic weight 26.9815; melting point 660.32°C; boiling point 2,519°C; specific gravity 2.70; valence 3. See Periodic Table.[alumin(a) + -(i)um.]American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.a?lu?mi?num (??lu m? n?m) n. 1. a silver-white metallic element, light in weight, ductile, malleable, and not readily corroded or tarnished: used in alloys and for lightweight products. Abbr.: alum.;Symbol: Al; at. wt.: 26.98; at. no.: 13; sp. gr.: 2.70 at 20°C. adj. 2. of, pertaining to, or containing aluminum. Also, esp. Brit., aluminium. [1812; alter. of earlier alumium. See alumina, -ium2] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.a·lu·mi·num (?-lo?o?m?-n?m) Symbol Al A lightweight, silvery-white metallic element that is easily shaped and a good conductor of electricity. It is the most abundant metal in the Earth’s crust and is used to make a wide variety of products from soda cans to airplane components. Atomic number 13. See Periodic Table.The American Heritage® Student Science Dictionary, Second Edition. Copyright © 2014 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.