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--- Shapes and Geometry
球体 kyūtai sphere 体 [body]   Ref. 球 [ball]
半周 hanshū semicircle   Ref. 周 [lap]
円周 enshū circumference   Ref. 周 [lap]
直径 chokkei diameter 直 [straight]  Ref. 径 [path]
直線 chokusen straight line 線 [line]  Ref. 直 [straight]