hydrogeologyPronunciation: /ˌhʌɪdrəʊdʒɪˈɒlədʒi/Definition of hydrogeology noun [mass noun] the branch of geology concerned with water occurring underground or on the surface of the earth. Derivatives hydrogeologicalPronunciation: /-dʒɪəˈlɒdʒɪk(ə)l/ adjective hydrogeologist noun hydrogeology in other Oxford dictionaries Definition of hydrogeology in the US English dictionary