'atomistical' originates from Greek, specifically the word 'atomos', where 'a-' meant 'not' and 'tomos' meant 'cut' (hence 'indivisible'); the English adjective is formed by combining 'atom' + the adjectival suffixes '-istic' and '-al'.

'atomistical' traces back through English formations such as 17th-century 'atomical' and 'atomistic'; Greek 'atomos' passed into Latin/Medieval Latin as 'atomus', then into English as 'atom' and later into adjectival forms 'atomistic'/'atomical' before yielding the modern form 'atomistical'.

Initially, it meant 'pertaining to indivisible particles' (literally 'of or relating to atoms'); over time it broadened to mean 'relating to the doctrine of atomism' and, figuratively, 'tending to treat things as discrete parts or fragments' (a reductionist sense).