G.I. (Adjective) — Of or relating to the stomach and intestines. ex. "a GI disorder"
G.I. (Noun) — A martial arts uniform (Judo, Karate, etc.).
G.I. (Noun) — A unit of magnetomotive force equal to 0.7958 ampere-turns.
G.I. (Verb) — Clean in preparation for inspection.