[syn: all-important(a), all important(p), crucial, essential, of the essence(p)]
The Collaborative International Dictionary of English v.0.48:
Crucial \Cru"cial\ (kr?"shal), a. [F. crucial, fr. L. crux,
   crucis, cross, torture. See Cross.]
   1. Having the form of a cross; appertaining to a cross;
      cruciform; intersecting; as, crucial ligaments; a crucial
      incision.
      [1913 Webster]
   2. Severe; trying or searching, as if bringing to the cross;
      decisive; as, a crucial test.
      [1913 Webster]
WordNet (r) 3.0 (2006):
crucial
    adj 1: of extreme importance; vital to the resolution of a
           crisis; "a crucial moment in his career"; "a crucial
           election"; "a crucial issue for women" [syn: crucial,
           important] [ant: noncrucial]
    2: having crucial relevance; "crucial to the case"; "relevant
       testimony"
    3: of the greatest importance; "the all-important subject of
       disarmament"; "crucial information"; "in chess cool nerves
       are of the essence" [syn: all-important(a), all
       important(p), crucial, essential, of the essence(p)]
Moby Thesaurus II by Grady Ward, 1.0:
55 Moby Thesaurus words for "crucial":
   aboriginal, acute, basal, basic, central, charged, clamorous,
   climacteric, compelling, critical, crying, deciding, decisive,
   desperate, dire, elemental, elementary, embryonic, emergent,
   essential, exigent, fundamental, generative, genetic, germinal,
   high-pressure, high-priority, imperative, imperious, important,
   in embryo, in ovo, insistent, instant, kairotic, loaded, major,
   momentous, necessary, original, pivotal, pregnant, pressing,
   primal, primary, primeval, primitive, primordial, pristine,
   protogenic, radical, rudimentary, seminal, urgent, vital