The Collaborative International Dictionary of English v.0.48:

Sift \Sift\, v. t. [imp. & p. p. Sifted; p. pr. & vb. n.
   Sifting.] [AS. siftan, from sife sieve. [root]151a. See
   Sieve.]
   1. To separate with a sieve, as the fine part of a substance
      from the coarse; as, to sift meal or flour; to sift
      powder; to sift sand or lime.
      [1913 Webster]

   2. To separate or part as if with a sieve.
      [1913 Webster]

            When yellow sands are sifted from below,
            The glittering billows give a golden show. --Dryden.
      [1913 Webster]

   3. To examine critically or minutely; to scrutinize.
      [1913 Webster]

            Sifting the very utmost sentence and syllable.
                                                  --Hooker.
      [1913 Webster]

            Opportunity I here have had
            To try thee, sift thee.               --Milton.
      [1913 Webster]

            Let him but narrowly sift his ideas.  --I. Taylor.
      [1913 Webster]

   To sift out, to search out with care, as if by sifting.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sifting
    n 1: the act of separating grain from chaff; "the winnowing was
         done by women" [syn: winnow, winnowing, sifting]

Moby Thesaurus II by Grady Ward, 1.0:

64 Moby Thesaurus words for "sifting":
   amassing evidence, appraisal, assessment, assortment, bolting,
   categorization, clarification, classification, close inquiry,
   colature, culling, department of investigation,
   destructive distillation, detection, detective work, distillation,
   edulcoration, elution, elutriation, essentialization, evaluation,
   exhaustive study, extraction, factoring, filtering, filtration,
   gauging, gradation, grouping, hearing, identification, indagation,
   investigation, investigative bureau, leaching,
   legislative investigation, legwork, lixiviation, percolation,
   perscrutation, placement, probe, purification, ranking, refinement,
   research, riddling, screening, selection, separation, sieving,
   sifting out, sleuthing, sorting, sorting out, spiritualization,
   straining, sublimation, subordination, taxonomy, triage, weighing,
   winnowing, witch-hunt