'animalculous' originates from New Latin, specifically the word 'animalculum' (a diminutive of 'animal' meaning 'living being'), plus the adjective-forming suffix '-ous' meaning 'full of' or 'pertaining to'.

'animalculous' changed from the New Latin diminutive 'animalculum' via the English noun 'animalcule' and eventually became the modern English word 'animalculous'.

Initially, it meant 'pertaining to tiny animals (animalcules),' and this meaning has largely remained the same, now understood as relating to microscopic organisms.