io I. noun (-s) Etymology: Latin, interjection, from Greek iō obsolete: a shout of joy or triumph < rocks, valleys, hills, with splitting ios ring — John Dryden & Nathaniel Lee > — often used interjectionally II. \ˈē(ˌ)ō\noun (-s) Etymology: Hawaiian : a large hawk (Buteo solitarius) that is the only indigenous raptorial bird of Hawaii