Aequanimitas

Aequanimitas, a Latin word derived from aequo animo, “with even mind”, meaning equanimity or calmness of mind.

Excerpts from Sir William Osler’s Valedictory Address at the University of Pennsylvania on May 1st, 1889:

I could have the heart to spare you, poor, careworn survivors of a hard struggle, so “lean and pale and leaden-eyed with study;” and my tender mercy constrains me to consider but two of the score of elements which may make or mar your lives—which may contribute to your success, or help you in the days of failure.
In the first place, in the physician or surgeon no quality takes rank with imperturbability, and I propose for a few minutes to direct your attention to this essential bodily virtue. Perhaps I may be able to give those of you, in whom it has not developed during the critical scenes of the past month, a hint or two of its importance, possibly a suggestion for its attainment. Imperturbability means coolness and presence of mind under all circumstances, calmness amid storm, clearness of judgment in moments of grave peril, immobility, impassiveness, or, to use an old and expressive word, phlegm. It is the quality which is most appreciated by the laity though often misunderstood by them; and the physician who has the misfortune to be without it, who betrays indecision and worry, and who shows that he is flustered and flurried in ordinary emergencies, loses rapidly the confidence of his patients.
…
In the second place, there is a mental equivalent to this bodily endowment, which is as important in our pilgrimage as imperturbability. Let me recall to your minds an incident related of that best of men and wisest of rulers, Antoninus Pius, who, as he lay dying, in his home at Loriam in Etruria, summed up the philosophy of life in the watchword, Aequanimitas. As for him, about to pass flammantia moenia mundi (the flaming rampart of the world), so for you, fresh from Clotho’s spindle, a calm equanimity is the desirable attitude. How difficult to attain, yet how necessary, in success as in failure!
…