staple

majority

aggregate, amount, entirety, quantum, sum, sum total, total, totality, whole

bottom, essence, essentiality, marrow, meat, nature, pith, quintessence, root, soul, stuff, substance

center, heart, hub, kernel, middle, nucleus, nut, seat

affair, argument, burden, crux, focus, gist, nub, pitch, point, purport

matter, motif, subject, text, theme, topic