The state or quality of being calm, composed, and in control of one's emotions.
From 'collected' (calm and composed) plus the suffix '-ness' (denoting abstract quality). The noun form captures the mental state of having gathered one's thoughts and emotions.
The noun 'collectedness' comes from the same root as 'collect'—it's the idea that calmness means you've gathered all your scattered thoughts and feelings back together in one controlled whole.
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