'unimitativeness' originates from English, formed by the negative prefix 'un-' (from Old English 'un-') plus the noun 'imitativeness', where 'imitate' ultimately comes from Latin 'imitari' meaning 'to copy, to mimic'.

'unimitativeness' is a modern English formation created by adding the prefix 'un-' to 'imitativeness' (itself formed from 'imitate' + '-ive' + '-ness'); 'imitate' came into English via Old French from Latin 'imitari'.

Initially, 'imitativeness' referred to a tendency to copy or mimic; adding the prefix 'un-' created the opposite sense — absence of that tendency — which is the current meaning of 'unimitativeness'.