gravamen

from The Collaborative International Dictionary of English v.0.48

from Bouvier's Law Dictionary, Revised 6th Ed (1856)

GRAVAMEN. The grievance complained of; the substantial cause, of the action. 
See Greenl. Ev. Sec. 66.

from Moby Thesaurus II by Grady Ward, 1.0

70 Moby Thesaurus words for "gravamen":
      axiom, bench mark, best part, better part, body, bulk,
      cardinal point, center, chief thing, climax, core, cornerstone,
      crisis, critical point, crux, elixir, essence, essential,
      essential matter, flower, focus, fundamental, generality, gist,
      great point, heart, high point, hypostasis, important thing,
      inner essence, issue, kernel, keystone, landmark, main body,
      main point, main thing, major part, majority, marrow, mass,
      material point, meat, milestone, most, nub, nucleus,
      nuts and bolts, pith, pivot, plurality, postulate, principle, quid,
      quiddity, quintessence, real issue, salient point, sap,
      sine qua non, soul, spirit, stuff, substance, substantive point,
      the bottom line, the nitty-gritty, the point, thrust,
      turning point