'micronucleus-free' originates from Modern English, specifically the compound of 'micronucleus' and 'free'. 'micronucleus' is formed from Greek 'mikros' (meaning 'small') + Latin/Neo-Latin 'nucleus' (meaning 'kernel' or 'small nut'), and 'free' originates from Old English 'frēo' (meaning 'not in bondage; without').

'micronucleus' was coined in scientific Neo-Latin/Modern English by combining Greek 'mikros' and Latin 'nucleus' to denote a 'small nucleus' or small extranuclear body; 'free' comes from Old English 'frēo' and passed into Middle and Modern English. The compound 'micronucleus-free' was formed in modern scientific English to describe the absence of micronuclei.

Initially, components had concrete senses ('mikros' = 'small', 'nucleus' = 'kernel/central body', 'free' = 'not bound'); over time in scientific usage 'micronucleus' came to mean the specific small extranuclear body observed in cells, and 'free' took on the compositional meaning 'without', giving the compound its current meaning 'without micronuclei'.