It’s used a lot in videogames, manga, and anime, dating back to Final Fantasy I using it for a kind of giant. The word originally comes from Greek mythology as another term for the gigantes.
When I was in grade school, me and my friends would often discuss Secret of Mana (originally titled Seiken Densetsu 2 in it’s Japanese release), another Square game like Final Fantasy. In it there are three boss-characters, elemental giants known as the Fire Gigas (actually the friendly earth-elemental Gnome in a corrupted form), Frost Gigas (Santa Claus in a corrupted form, and no I am not joking), and Thunder Gigas (not anyone’s corrupted form, IIRC).
I and most of my friends always assumed it was pronounced “gee-gess,” while a few pronounced it “JEE-gess.” I’m using g for a hard g, and j for the sound in “george.” Also capitalizing to show emphasis, where there’s any.
But I got to wondering, how would the Greeks have pronounced it? And what would people today consider correct?