The relaxation and widening of the pupil of the eye, or the stage in the pupil's movement when it expands.
From Greek koro- (pupil) and diastole (drawing apart, expansion), mirroring the medical term diastole used in cardiology to describe heart expansion.
Just like the heart has systole and diastole, ancient Greeks named the pupil's expansion phases using the same beautiful parallel terminology—it shows how languages systematize observations about movement and change.
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