anatomical entity An anatomical entity is a material entity that is part of a multicellular organism, and which is large enough so that it forms an identifiable structure in the organism. Specifically, it excludes granular parts of the organism, such as atoms, molecules, cells, which can be removed from the organism without affecting it. It is defined as the union of 'multi-tissue structure', 'body substance' and 'portion of tissue' anatomical entity