'unimitative' originates from English, formed by the negative prefix 'un-' + the adjective 'imitative' (from Latin 'imitativus', from 'imitari' meaning 'to imitate'), where 'un-' meant 'not' and 'imitative' related to imitation.

'imitative' entered English via Middle English and Old French from Latin 'imitativus' (from 'imitari'). In Modern English the productive negative prefix 'un-' was added to form 'unimitative', giving the modern adjective.

Initially, the root 'imitative' meant 'relating to imitation'; with the addition of 'un-' the meaning became 'not imitative, not copying', and this negative sense is the modern usage.