'atom' originates from Ancient Greek, specifically the word 'atomos', where the prefix 'a-' meant 'not' and 'tomos' meant 'cut'.

'atom' changed from the Ancient Greek word 'atomos' into Latin and Medieval Latin forms such as 'atomus', entered Old French and Middle English, and eventually became the modern English word 'atom'.

Initially, it meant 'indivisible' or 'uncuttable'. Over time, especially after developments in chemistry and physics, it came to mean 'the smallest unit of a chemical element' even though atoms are now known to be divisible into subatomic particles.