This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

• Lexulous
• Wordscraper
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n. The quality of being calm and even-tempered; composure.

n. The state of being calm, stable and composed, especially under stress.

n. Evenness of mind; that calm temper or firmness of mind which is not easily elated or depressed; patience; calmness; composure.

n. Evenness of mind or temper; calmness or firmness, especially under conditions adapted to excite great emotion; a state of resistance to elation, depression, anger, etc.

n. steadiness of mind under stress

"We weren’t rolling in money, but we certainly had enough to live well, and I approached my thirties with a certain … no, I really don’t want to use the word equanimity here, even though it’s apt."

temperament    disposition   

calmness   

equanimous   

cool    poise    placidity    assuredness    tranquillity    serenity    sang-froid    quiet    tranquility    aplomb   

patience    calmness    composure    evenness    calm    peace   

anonymity    unanimity   

composure    fortitude    cheerfulness    self-control    self-possession    gentleness    placidity    resignation    coolness    contentment