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.
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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]