1 loose white jacket worn in Judo
2 A US Army soldier – 1930s (originally denoting equipment supplied to US forces): abbreviation of government (or general) issue.
3 abbreviation for glycemic index
4 abbreviation for gastrointestinal tract
“Gee,” said Gio as he cinched the white belt around his gi to prepare for the bout against another army GI. He hoped his pre-match high GI carbo-load would not get clogged in his GI tract.