A fork of Rural Dictionary
Begrudging benevolence.
The lottery winner showed quite a bit of magnanimosity when he donated his winnings towards his local disaster relief, after the flood. He didn't want to, but he knew it was the right thing to do.
A blend of animosity and magnanimous, an insincere enthusiasm or friendliness hiding ill intent.
Magnanimosity is smiling at someone while you plot their death.