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(mathematics) A surface in three dimensions consisting of all points equidistant from a center. .
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An object which appears to be bounded by a sphere; a round object, a ball.
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(astronomy, now rare) The celestial sphere: the edge of the heavens, imagined as a hollow globe within which celestial bodies appear to be embedded.
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(historical, astronomy, mythology) Any of the concentric hollow transparent globes formerly believed to rotate around the Earth, and which carried the heavenly bodies; there were originally believed to be eight, and later nine and ten; friction between them was thought to cause a harmonious sound (the music of the spheres).
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(mythology) An area of activity for a planet; or by extension, an area of influence for a god, hero etc.
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(figuratively) The region in which something or someone is active; one's province, domain.
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The natural, normal, or proper place (of something).
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(geometry) The set of all points in three-dimensional Euclidean space (or n-dimensional space, in topology) that are a fixed distance from a fixed point .
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(logic, dated) The domain of reference of a proposition, subject, or predicate, or the totality of the particular subjects to which it applies.