1. A large trash receptacle made from galvanized iron (GI) used by the military during World War I. Primarily heard in US, South Africa. Our uniforms became so infested with lice after living in the trenches that we were all ordered to dump them into the GI cans at the edge of the encampment.
2. World War I military slang for a large German artillery shell. Primarily heard in US, South Africa. The first time you hear the blast it scares you half to death, but before long, the sound of GI cans dropping around you becomes part of the daily routine.
See also: can