'non-identical' is formed from the negative prefix 'non' and the adjective 'identical'. 'non' originates from Latin, specifically the word 'non', where 'non' meant 'not'. 'identical' originates from French, specifically the word 'identique', which comes from Late Latin 'identicus', related to Latin 'idem' meaning 'the same'.

'identical' changed from Greek 'identikos' into Late Latin 'identicus', then into French 'identique' (Middle French) and entered English as 'identical'; the prefix 'non-' was attached in English (and earlier via Old French/Latin usage) to create the compound 'non-identical'.

Initially, 'identical' meant 'the same' (from Latin 'idem'), and the addition of the negating prefix 'non-' has consistently produced the meaning 'not the same'; this basic negated sense has remained stable though the compound is often used in more technical or formal contexts.