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)