Aluminum is the American spelling and aluminium is the British spelling for this ductile, malleable silver-white metal.
In 1812, its discoverer, Sir H. Davy, first called the metal alumium but then modified the word. This is one of a number of spelling differences between British and American English, such as: aeroplane/airplane, aesthetics/esthetics, colour/color, encyclopaedia/encyclopedia, paralyse/paralyze. The principle differences are: 1) a final -l is always doubled after one vowel in stressed and unstressed syllables in British English, but usually only in stressed syllables in American English; 2) some words end in -tre in British English and -terin American English; 3) some words end in -ogue in British English and -og in American English; 4) some words end in -our in British English and -or in American English; and 5) some verbs end in -ize or -ise in British English, but only in -ize in American English. In common speech, some 4,000 words are used differently in the UK from the United States.