'micronuclear' originates from the combining form 'micro-' and the adjective 'nuclear'. 'micro-' comes from Greek, specifically the word 'mikros', where 'mikros' meant 'small'. 'nuclear' comes from Latin 'nucleus' (via English), ultimately from Greek 'karyon' meaning 'kernel'.

'micronuclear' was formed in modern scientific English by combining the Greek-derived prefix 'micro-' (via New Latin/scientific coinage) with the existing English adjective 'nuclear' (from Latin 'nucleus', through Middle/Modern English). The compound arose in biological usage to describe structures pertaining to a small nucleus.

Initially it literally meant 'pertaining to a small nucleus'; over time the term became specialized in cell biology to refer specifically to features or functions of the micronucleus (as opposed to the macronucleus) in certain protists.