What is Animus?

Legal Definition
The intent; the mind with which a thing is done, as animus. cancellandi, the intention of cancelling; animus farandi, the intention of stealing; animus maiaendi; the intention of remaining; auimus morandi, the intention or purpose of delaying.

2. Whether the act of a man, when in appearance criminal, be so or not, depends upon the intention with which it was done. Vide Intention.
-- Bouviers Law Dictionary
Legal Definition
Lat. Mind; intention; disposition; design; will. Animo, (q. v.;) with the intention or design. These terms are derived from the civil law.
-- Black's Law Dictionary
Legal Definition
Mind; intent.
-- Ballentine's Law Dictionary