The Collaborative International Dictionary of English v.0.48:

Requisite \Req"ui*site\ (r?k"w?-z?t), n.
   That which is required, or is necessary; something
   indispensable.
   [1913 Webster]

         God, on his part, has declared the requisites on ours;
         what we must do to obtain blessings, is the great
         business of us all to know.              --Wake.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Requisite \Req"ui*site\, a. [L. requisitus, p. p. requirere;
   pref. re- re- + quaerere to ask. See Require.]
   Required by the nature of things, or by circumstances; so
   needful that it can not be dispensed with; necessary;
   indispensable.
   [1913 Webster]

         All truth requisite for men to know.     --Milton.
   [1913 Webster]

   Syn: Necessary; needful; indispensable; essential.
        [1913 Webster] -- Req"ui*site*ly, adv. --
        Req"ui*site*ness, n.
        [1913 Webster]

WordNet (r) 3.0 (2006):

requisite
    adj 1: necessary for relief or supply; "provided them with all
           things needful" [syn: needed, needful, required,
           requisite]
    n 1: anything indispensable; "food and shelter are necessities
         of life"; "the essentials of the good life"; "allow farmers
         to buy their requirements under favorable conditions"; "a
         place where the requisites of water fuel and fodder can be
         obtained" [syn: necessity, essential, requirement,
         requisite, necessary] [ant: inessential,
         nonessential]

Moby Thesaurus II by Grady Ward, 1.0:

72 Moby Thesaurus words for "requisite":
   appropriate, bare necessities, boundary condition, call for,
   called for, catch, clause, condign, condition, demand, demand for,
   deserved, desideration, desideratum, donnee, due, escalator clause,
   escape clause, escape hatch, essential, essentials, fine print,
   given, grounds, indicated, indispensable, irreducible,
   irreductible, irreplaceable, joker, kicker, limiting condition,
   merited, must, must item, necessaries, necessary, necessities,
   necessity, need, need for, needed, needful, obligation, occasion,
   parameter, prerequirement, prerequisite, provision, provisions,
   proviso, required, requirement, requisition, right, rightful,
   saving clause, sine qua non, small print, specification,
   stipulation, string, suitable, terms, the necessary, the needful,
   ultimatum, unforgoable, vital, want, wanted, whereas