'microfaunistic' originates from a compound of Greek and Latin elements: 'micro-' from Greek 'mikros' meaning 'small' and 'fauna' from Latin 'Fauna' (used to mean 'animal life'), with the adjectival suffix '-istic' (via Greek/Latin '-istikos') forming 'pertaining to'.

'micro-' (Greek 'mikros') and Latin 'fauna' were combined in modern scientific English; 'faunistic' arose in the 19th century to describe matters relating to fauna, and the compound 'microfaunistic' appeared later in scientific literature to specify very small fauna or their study.

Initially the elements meant 'small' and 'animal life'; over time the compound came to mean specifically 'relating to very small animals or the study of them', a specialized scientific sense that remains today.