The Collaborative International Dictionary of English v.0.48:

Probe \Probe\, v. t. [imp. & p. p. Probed; p. pr. & vb. n.
   Probing.] [L. probare to try, examine. See Prove.]
   [1913 Webster]
   1. To examine, as a wound, an ulcer, or some cavity of the
      body, with a probe.
      [1913 Webster]

   2. Fig.: to search to the bottom; to scrutinize or examine
      thoroughly. --Dryden.
      [1913 Webster]

            The growing disposition to probe the legality of all
            acts, of the crown.                   --Hallam.
      [1913 Webster]

WordNet (r) 3.0 (2006):

probing
    adj 1: diligent and thorough in inquiry or investigation; "a
           probing inquiry"; "a searching investigation of their
           past dealings" [syn: inquisitory, probing,
           searching]

Moby Thesaurus II by Grady Ward, 1.0:

45 Moby Thesaurus words for "probing":
   Socratic method, asking, bringing into question,
   catechetical method, catechization, catechizing, challenge,
   deepening, delving, depression, digging, dispute, drilling,
   examination, excavation, fishing, in search of, inquest, inquiring,
   inquisition, interpellation, interrogation, investigation,
   loaded for bear, looking for, lowering, mining, nosy, out for,
   out for bear, poking, probe, prying, pumping, querying, quest,
   questioning, quiz, quizzing, research, searching, seeking, sinkage,
   sinking, tunneling