'nucleus' originates from Latin, specifically the word 'nucleus', where 'nucleus' meant 'kernel' or 'core'.

'nucleus' passed into English from Latin (via Medieval Latin) as 'nucleus' and the modern English singular became 'nucleus' with the regular Latin plural 'nuclei'.

Initially, it meant 'kernel' or 'core', and over time it evolved into the current meanings including 'central part of an atom, cell, or organization'.