gee-fat, n. — Green’s Dictionary of Slang

gee-fat n.

[? Chi. gee-yen, the residue left in an opium pipe]

(US drugs) narcotics, usu. the residue of opium.

1937		B. Dai Opium Addiction in Chicago 199: Gee fat. The lining of an opium pipe.
1949		Monteleone Criminal Sl. (rev. edn).
1959		J.E. Schmidt Narcotics Lingo and Lore.