半圆圆周率 semiciecle

圆、圆周 Circle

圆弧/圆周 Arc/Circle

不圆的圆周 out-of-round circle

半圆上的圆周角是直角 angle in semi-circle

圆周钻孔圆头螺母 round nut with drilled holes in side

圆周圆周 Circumference

圆周点圆 circle-point