hy·dro I. \ˈhī(ˌ)drō\noun (-s) 1.[short for hydropathic (II) ]Britain a.: a hotel that caters to people taking a water cure b.: an establishment that furnishes water cures : spa 2.[short for hydroelectric] a.chiefly Canada: hydroelectric power b.: a hydroelectric power plant II. adjective Etymology: by shortening : hydroelectric < hydro power > III. adjective Etymology:hydr- : hydrogen : combined with hydrogen < hydro derivatives >