G.I. — Wordorigins.org
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6 December 2023 A G.I. is an American soldier, and G.I. is used as an adjective denoting things related to the U.S. military. The term came into its own during World War II, but its origins go back somewhat further. G.I. started out as a U.S. military abbreviation for galvanized iron. A War

TIL that “G.I.” originally referred to objects made from galvanized iron from WWI on, before it was reinterpretated as "government issue ", and by WWII, applied to American soldiers.