It is the hypothetical source of/evidence for its existence is provided by: Greek oinos "ace (on dice);" Latin unus "one;" Old Persian aivam; Old Church Slavonic -inu, ino-; Lithuanian vienas; Old Irish oin; Breton un "one;" Old English an, German ein, Gothic ains "one."
1820, "temper" (usually in a hostile sense), from Latin animus "rational soul, mind, life, mental powers, consciousness, sensibility; courage, desire," related to anima "living being, soul, mind, disposition, passion, courage, anger, spirit, feeling," from PIE root *ane- "to breathe."
It has no plural. As a term in Jungian psychology for the masculine component of a feminine personality, it dates from 1923 (compare anima). For sense development in Latin, compare Old Norse andi "breath, breathing; current of air; aspiration in speech;" also "soul, spirit, spiritual being."