英语词源字典 - 在线词源网站

GI [GI 词源字典]: GI: [20] GI originated, around the beginning of the 20th century, as a US abbreviation of galvanized iron. It was soon in common use in the military, in contexts such as GI can, and the idea seems to have got about that it stood for not galvanized iron but government issue. This misconception propelled it into such combinations as GI shoe, GI soap and (facetiously) GI soldier. By the 1930s this had been shortened to simply GI, designating an enlisted man in the US Army.
[GI etymology, GI origin, 英语词源]
facetious (adj.): 1590s, from French facétieux (16c.), from facétie "a joke" (15c.), from Latin facetiae "jests, witticisms" (singular facetia), from facetus "witty, elegant, fine, courteous," which is of unknown origin, perhaps related to facis "torch."

Formerly often in a good sense, "witty, amusing," but later implying a desire to be amusing that is often intrusive or ill-timed. Related: Facetiously; facetiousness. "Facetiæ in booksellers' catalogues, is, like curious, a euphemism for erotica." [Fowler]
Gaul (n.): 1560s, "an inhabitant of ancient Gaul," from French Gaule, from Latin Gallia, from Gallus "a Gaul." Also used somewhat facetiously for "a Frenchman." Gauloise, the popular brand of French cigarettes, dates to 1910.