"A defect of speech; especially stammering", Mid 19th cent. From post-classical Latin psellismus from Hellenistic Greek ψελλισμός action or fact of stammering from ancient Greek ψελλίζειν to stammer (from ψελλός (adjective) stammering (of imitative origin, with expressive gemination and a suffix -λό- frequently used to designate infirmities) + -ίζειν) + -ισμός.[psellism etymology, psellism origin, 英语词源]