köken: The 連用形 (ren'yōkei, “continuative or stem form”) of verb 欲張る (yokubaru, “to be intensely greedy”). Appears in texts from 1813. Ultimately, likely a shift from older synonym 欲ぼり (yokubori), dating to 1519.
köken: Presumably a derivation from Late Latin gaza (“treasury, wealth, riches”), from Ancient Greek γάζα (gáza, “treasury, treasure”), from Old Median *ganǰam (“treasure”).