Steadiness of mind under stress:
— He accepted their problems with composure and she with equanimity.

synonyms: calm, calmness, equanimity.

Roget 826: inexcitability^†, imperturbability, inirritability^†; even temper, tranquil mind, dispassion; tolerance, patience, coolth [Coll.].    passiveness etc. (physical inertness) 172; hebetude^†, hebetation^†; impassibility etc. (insensibility) 823; stupefaction.    coolness, calmness etc. adj.; composure, placidity, indisturbance^†, imperturbation^†, sang froid [Fr.], tranquility, serenity; quiet, quietude; peace of mind, mental calmness.    staidness etc. adj.; gravity, sobriety, Quakerism^†; philosophy, equanimity, stoicism, command of temper; self-possession, self-control, self-command, self-restraint, ice water in one's veins; presence of mind.    submission etc. 725; resignation; sufferance, supportance^†, endurance, longsufferance^†, forbearance; longanimity^†; fortitude; patience of Job, patience on a monument" [Twelfth Night], patience 'sovereign o'er transmuted ill'" [Johnson]; moderation; repression of feelings, subjugation of feeling; restraint etc. 751.    tranquillization etc. (moderation) 174^†.    ... show more

Dutch: gelijkmoedigheid, gelatenheid, kalmte, zelfbeheersing, beheersing, bedaardheid
Polish: opanowanie