'microanimal' originates from a combination of Greek and Latin, specifically the Greek word 'mikros' and the Latin word 'animalis', where 'mikros' meant 'small' and 'animalis' meant 'having breath; a living being'.

'microanimal' was formed in Modern English as a compound from the prefix 'micro-' (from Greek via New/Modern scientific coinage) and the noun 'animal' (from Latin 'animalis'), following the pattern of scientific compounds in New/Modern Latin and English.

Initially it simply meant 'a small animal', but over time its usage has specialized to refer especially to animals that are microscopic or nearly microscopic, often studied in microbiology and soil/aquatic ecology.