Here are some of Aquinas' teachings on magnanimity:
Magnanimity is the expansion of the soul to great things.
It is characteristic of magnanimous people to be more solicitous about the truth than about the opinions of others.
It is a mark of magnanimous people to speak and work openly. . . . That people hide what they do and say arises from the fear of others.
Magnanimous people deliberately determine to forget injuries they have suffered.
Magnanimity is part of the virtue of courage or fortitude.
Magnanimity strengthens a person to take on good tasks.— Thomas Aquinas, Confessions by Matthew Fox