'undividable' originates from Modern English, specifically a combination of the prefix 'un-' and the adjective 'dividable', where 'un-' meant 'not' and the Latin root 'dividere' meant 'to separate, to divide'.

'undividable' developed by adding the English negative prefix 'un-' to forms related to 'divide' (compare 'divisible' from Latin 'divisibilis'), with 'divide' itself coming from Latin 'dividere' via Old French 'diviser' and Middle English 'dividen'.

Initially, it meant 'not capable of being divided'; over time the meaning has largely remained the same as the modern meaning 'not able to be divided.'