From The Collaborative International Dictionary of English v.0.48:

Searching \Search"ing\, a.
   Exploring thoroughly; scrutinizing; penetrating; trying; as,
   a searching discourse; a searching eye. "Piercing, searching,
   biting, cold." --Dickens.
   [1913 Webster] -- Search"ing*ly, adv. -- Search"ing*ness,
   n.
   [1913 Webster]

From The Collaborative International Dictionary of English v.0.48:

Search \Search\, v. t. [imp. & p. p. Searched; p. pr. & vb. n.
   Searching.] [OE. serchen, cerchen, OF. cerchier, F.
   chercher, L. circare to go about, fr. L. circum, circa,
   around. See Circle.]
   1. To look over or through, for the purpose of finding
      something; to examine; to explore; as, to search the city.
      "Search the Scriptures." --John v. 39.
      [1913 Webster]

            They are come to search the house.    --Shak.
      [1913 Webster]

            Search me, O God, and know my heart.  --Ps. cxxxix.
                                                  23.
      [1913 Webster]

   2. To inquire after; to look for; to seek.
      [1913 Webster]

            I will both search my sheep, and seek them out.
                                                  --Ezek. xxxiv.
                                                  11.
      [1913 Webster]

            Enough is left besides to search and know. --Milton.
      [1913 Webster]

   3. To examine or explore by feeling with an instrument; to
      probe; as, to search a wound.
      [1913 Webster]

   4. To examine; to try; to put to the test.
      [1913 Webster]

   To search out, to seek till found; to find by seeking; as,
      to search out truth.
      [1913 Webster]

   Syn: To explore; examine; scrutinize; seek; investigate; pry
        into; inquire.
        [1913 Webster]

From WordNet (r) 2.0:

searching
     adj 1: diligent and thorough in inquiry or investigation; "a
            probing inquiry"; "a searching investigation of their
            past dealings" [syn: inquisitory, probing]
     2: having keenness and forcefulness and penetration in thought,
        expression, or intellect; "searching insights"; "trenchant
        criticism" [syn: trenchant]
     3: exploring thoroughly

From Moby Thesaurus II by Grady Ward, 1.0:

58 Moby Thesaurus words for "searching":
   chase, cynegetic, delving, digging, dogging, domiciliary visit,
   dragnet, exploration, fishing, follow, follow-up, following,
   forage, frisk, halieutic, house-search, hue and cry, hunt, hunting,
   in full cry, in hot pursuit, in pursuit, in search of,
   loaded for bear, looking for, nosy, out for, out for bear,
   perquisition, piscatorial, piscatory, poking, posse, probe,
   probing, prosecution, prying, pursuance, pursuant, pursuing,
   pursuit, quest, questing, ransacking, rummage, search,
   search party, search warrant, search-and-destroy operation,
   seeking, shadowing, stalk, stalking, still hunt, tracking,
   tracking down, trailing, turning over