animus (n.) Look up animus at Dictionary.com
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. For sense development in Latin, compare Old Norse andi "breath, breathing; current of air; aspiration in speech; soul, spirit, spiritual being."