prednisone UK /ˈpɹɛd.nɪ.zəʊn/US /ˈpɹɛd.nɪˌsoʊn/ noun1 •A glucocorticoid C₂₁H₂₆O₅ that is a dehydrogenated analog of cortisone, used to relieve rheumatic and allergic conditions and to treat leukemia. formsprednisones