Definition of GI:
(adj) :
given to a soldier by the army (as an item), rather than brought from home; or used by the army (as a procedure), and different from its
civilian counterpart
"soldiers counted cadence by chanting: "GI brush / And GI comb / Gee, I wish that I was home!""
(n) :
a member of the U.S. military; one who is
demanding and
strict, in the manner of a stereotypical member of the military
(v) :
to
clean aggressively
"top, get the unit to GI this AO before the old man arrives."
"I was queasy after my upper GI series, but it far outshone the lower one."