animalcule n.

early 14c., "any sentient living creature" (including humans), from Latin animale "living being, being which breathes," noun use of neuter of animalis (adj.) "animate, living; of the air," from anima "breath, soul; a current of air" (from PIE root *ane- "to breathe;" for sense development, compare deer).

A rare word in English before c. 1600, and not in KJV (1611). Commonly only of non-human creatures. It drove out the older beast in common usage. Used derisively of brutish humans (in which the "animal," or non-rational, non-spiritual nature is ascendant) from 1580s.

Quid est homo? A dedlych best and resonable, animal racionale. ["Battlefield Grammar," c. 1450]

Proto-Indo-European root meaning "to breathe."

It forms all or part of: anemo-; anemometer; anemone; anima; animadversion; animadvert; animal; animalcule; animalistic; animate; animation; animatronic; anime; animism; animosity; animus; Enid; equanimity; longanimity; magnanimous; pusillanimous; unanimous.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit aniti "breathes;" Greek anemos "wind;" Latin animus "rational soul, mind, life, mental powers, consciousness, sensibility; courage, desire," anima "living being, soul, mind, disposition, passion, courage, anger, spirit, feeling;" Old Irish anal, Welsh anadl "breath," Old Irish animm "soul;" Gothic uzanan "to exhale," Old Norse anda "to breathe," Old English eðian "to breathe;" Old Church Slavonic vonja "smell, breath;" Armenian anjn "soul."