The Collaborative International Dictionary of English v.0.48:

Thorough bass \Thor"ough bass`\ (Mus.)
   The representation of chords by figures placed under the
   base; figured bass; basso continuo; -- sometimes used as
   synonymous with harmony.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Bass \Bass\ (b[=a]s), n. [F. basse, fr. bas low. See Base, a.]
   [1913 Webster]
   1. A bass, or deep, sound or tone.
      [1913 Webster]

   2. (Mus.)
      (a) The lowest part in a musical composition.
      (b) One who sings, or the instrument which plays, bass.
          [Written also base.]
          [1913 Webster]

   Thorough bass. See Thorough bass.
      [1913 Webster]

WordNet (r) 3.0 (2006):

thorough bass
    n 1: a bass part written out in full and accompanied by numbers
         to indicate the chords to be played [syn: figured bass,
         basso continuo, continuo, thorough bass]