Gỵa, pronounced dịa, is the only remaining instance of "gy-" in modern Vietnamese and one of only a few words ending in "-ya" (another being khuya). Some writers instead use the less exotic spelling gịa, which is not to be confused with giạ (“grain measure; about 40 liters or 30 kilograms of rice”) or dạ (“yes”).
http://en.wiktionary.org/wiki/gi%E1%BA%B7t_g%E1%BB%B5a