The Collaborative International Dictionary of English v.0.48:

Thorough \Thor"ough\, prep. [See Through.]
   Through. [Obs.] --Spenser. Shak.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Thorough \Thor"ough\, a.
   1. Passing through; as, thorough lights in a house. [Obs.]
      [1913 Webster]

   2. Passing through or to the end; hence, complete; perfect;
      as, a thorough reformation; thorough work; a thorough
      translator; a thorough poet.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Thorough \Thor"ough\, adv.
   1. Thoroughly. [Obs. or Colloq.] --Chaucer.
      [1913 Webster]

   2. Through. [Obs.] --Shak.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Thorough \Thor"ough\, n.
   A furrow between two ridges, to drain off the surface water.
   [Prov. Eng.] --Halliwell.
   [1913 Webster]

WordNet (r) 3.0 (2006):

thorough
    adj 1: painstakingly careful and accurate; "our accountant is
           thorough"; "thorough research"
    2: performed comprehensively and completely; "an exhaustive
       study"; "made a thorough search"; "thoroughgoing research"
       [syn: exhaustive, thorough, thoroughgoing]

Moby Thesaurus II by Grady Ward, 1.0:

150 Moby Thesaurus words for "thorough":
   absolute, all-embracing, all-encompassing, all-inclusive, all-out,
   all-pervading, arrant, assiduous, blow-by-blow, born, broad-based,
   canny, careful, cautious, chronic, circumspect, classical, clean,
   clear, complete, comprehensive, confirmed, congenital,
   conscientious, consummate, crass, decided, deep-dyed, deep-fixed,
   deep-rooted, deep-seated, deep-set, deep-settled, definitive,
   deliberate, detailed, diligent, discreet, downright,
   dyed-in-the-wool, egregious, elaborate, encyclopedic, established,
   exhaustive, extensive, fast, full, full-dress, fully realized,
   gingerly, glaring, gross, guarded, heedful, hesitant, implanted,
   incorrigible, inculcated, industrious, infixed, ingrained,
   instilled, intensive, intolerable, inveterate, irreversible,
   itemized, judicious, leaving out nothing, long-established,
   methodical, meticulous, mindful, minute, noncommittal, omnibus,
   omnipresent, on guard, operose, out-and-out, outright,
   overlooking no possibility, painstaking, particular,
   particularized, pawky, perfect, pervasive, plain, plumb, polished,
   politic, positive, precious, profound, pronounced, proper, prudent,
   pure, radical, rank, regardful, regular, rooted, safe, scrupulous,
   sedulous, set, settled, settled in habit, shattering, sheer,
   shocking, slow to act, stark, stark-staring, straight, superlative,
   surpassing, sweeping, tentative, the veriest, thoroughgoing,
   through-and-through, total, ubiquitous, unadventurous, unalloyed,
   unbearable, uncommunicative, unconditional, unconscionable,
   undaring, undeniable, undiluted, unenterprising, unequivocal,
   universal, unmitigated, unmixed, unprecipitate, unqualified,
   unrelieved, unreserved, unrestricted, unspoiled, utter, veritable,
   wholesale