apple core; core of an apple
padding; lining; foundation
Chinese water spinach (Ipomoea aquatica); ong choy; kang kong; water morning glory; water convolvulus; swamp cabbage
thick obi sash; sash padding
pencil lead case (for a mechanical pencil)
eccentricity (in mechanics, electronics, etc.)
pencil lead case (for mechanical pencil)
collar core (stiff fabric, etc. inside a collar)