animus

Animus, animi is second declension masculine, and it has a close relative that does a different job: anima, animae, first declension feminine, is the breath and then the soul, the thing that leaves you when you die. Animus is the mind at work: thought, will, temper, intention, feeling, courage. When a Roman says he has something in animo he means he has decided to do it.

The idioms are worth taking whole rather than piece by piece. Bono animo esse is to be in good heart; aequo animo, "with a level mind", is the standard phrase for taking bad news calmly; animum advertere, contracted to animadvertere, is to turn the mind towards something and so to notice, and then in officialese to punish. In the plural animi often means high spirits or courage, and in the wrong mood arrogance.

English took animate, unanimous, magnanimous, equanimity, animosity and animal, though that last one comes through anima and the breath rather than the mind.