1 a: not open b:enclosedc: composed entirely of closed tubes or vessels <a closed circulatory system> 2 a: forming a self-contained unit allowing no additions <closed association>b (1): traced by a moving point that returns to an arbitrary starting point <closed curve>; also: so formed that every plane section is a closed curve <closed surface>(2): characterized by mathematical elements that when subjected to an operation produce only elements of the same set <the set of whole numbers is closed under addition and multiplication>(3): containing all the limit points of every possible subset <a closed interval contains its endpoints>c: characterized by continuous return and reuse of the working substance <a closed cooling system>dof a racecourse: having the same starting and finishing point 3 a: confined to a few <closed membership>b: excluding participation of outsiders or witnesses : conducted in strict secrecy c: rigidly excluding outside influence <a closed mind> 4: ending in a consonant <closed syllable>