erythropoietinPronunciation: /ɪˌrɪθrə(ʊ)pɔɪˈɛtɪn/Definition of erythropoietin noun [mass noun] Biochemistry a hormone secreted by the kidneys that increases the rate of production of red blood cells in response to falling levels of oxygen in the tissues. erythropoietin in other Oxford dictionaries Definition of erythropoietin in the US English dictionary