ellipse
楕 centers on the geometric shape of an ellipse: a flattened circle or oval.
楕 is a phono-semantic compound: 木 (tree, wood) suggests a material or shape, and the right side (a simplified form related to 隋) likely contributes the sound ダ. The exact historical development of the right-side component is uncertain.
Picture a wooden (木) frame shaped into an ellipse. The right side looks like a squashed oval with a line through it, reinforcing the elliptical shape.
For ダ, imagine drawing an ellipse in the dark: dark -> ダ, and the wooden frame helps you trace the oval shape.
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ellipse; oval
superellipse
spheroid
ellipsoid body
elliptic geometry; Riemannian geometry
elliptical shape; oval shape
elliptic curve
elliptical orbit
elliptical galaxy
elliptic function
ellipsoid
hyperelliptic function