What is another word for "pith"?

Roget's Thesaurus (1911) lists these synonyms for "pith": abdomen, abdominal, axial, axis, azygous, backbone, belly, bosom, breast, bring, buoyancy, cave, center, central, centrality, centralization, centralize, centrally, centrical, circumscribe, coeliac, column, concavity, concentrate, concentration, concentric, contents, converge, convergence, core, deep, domestic, endemic, entrails, eye, family, focal, focus, gravity, gut.