Magnanimity, if you take the word and break it down to its Latin parts, literally means "largeness of soul." According to Aristotle (he used the Greek equivalent megalopsychia), magnanimity is the virtue of being great of mind and heart, encompassing a refusal to be petty, a willingness to face danger, and to engage in actions for unselfish and noble purposes. It's not uncommon for a magnanimous person to risk death and difficulty for the sake of a higher cause.
St. Thomas Aquinas' view of magnanimity is similar to Aristotle's. It also involves a sense of greatness and nobility, but it is more focused on the idea of supernatural hope and the pursuit of eternal honors - not honors in the sense of gaining in some earthly way, such as accolades accorded by man. So, Aquinas' concept of magnanimity is more closely tied to the idea of theological hope, whereas Aristotle's concept is more focused on the idea of human excellence.
For Aristotle, a magnanimous person could be a great military leader, or a great statesman, or a great philosopher. For St. Thomas, a magnanimous person is anyone who sacrifices their own will for the good of another person.
In other words, a magnanimous Christian is none other than a saint!
Fortunately for you and me, since only a handful of historical figures could ever qualify to be magnanimous under Aristotle's definition, according to St. Thomas any Christian who chooses sacrificial love has a great soul and is magnanimous. If you live your life to help others and if you pray for others, then you are already living magnanimously. Better still, the more sufferings you endure to love others, the larger your soul becomes.
Continue the daily fight to expand your soul, to choose love no matter the difficulty, and every day your soul will increase, until it takes on the dimensions of the Soul of Jesus Christ.