Synonyms and related words :
axiom, cavil, center, core, dodge, elixir, essence, essential, flower, focus, fundamental, gist, gravamen, heart, hypostasis, inner essence, jesuitism, kernel, marrow, meat, nub, nucleus, nuts and bolts, pith, postulate, principle, quibble, quid, quillet, quintessence, quip, quirk, quodlibet, sap, shuffle, soul, spirit, stuff, substance, the nitty-gritty