The Dictionary of Soldier Talk says GI was used for the words galvanized iron in a publication about the vehicles of the early twentieth century.
VOA: special.2010.03.07
Well,no one really knows. The Oxford English Dictionary lists about six hundred fifteen thousand words.
VOA: special.2011.01.12
Here is a recording of several words in the dictionary.
VOA: special.2009.12.02
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