1. 
[syn: all-important(a), all important(p), crucial, essential, of the essence(p)]
The Collaborative International Dictionary of English v.0.48:
all-important \all-important\ adj. prenom.
   1. of the greatest importance. the all-important subject of
      disarmament
   Syn: all important(predicate), crucial, essential, of the
        essence(predicate).
        [WordNet 1.5]
WordNet (r) 3.0 (2006):
all-important
    adj 1: 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)]