The Collaborative International Dictionary of English v.0.48:

Thesis \The"sis\, n.; pl. Theses. [L., fr. Gr. ?, fr. ? to
   place, set. See Do, and cf. Anathema, Apothecary,
   Epithet, Hypothesis, Parenthesis, Theme, Tick a
   cover.]
   1. A position or proposition which a person advances and
      offers to maintain, or which is actually maintained by
      argument.
      [1913 Webster]

   2. Hence, an essay or dissertation written upon specific or
      definite theme; especially, an essay presented by a
      candidate for a diploma or degree.
      [1913 Webster]

            I told them of the grave, becoming, and sublime
            deportment they should assume upon this mystical
            occasion, and read them two homilies and a thesis of
            my own composing, to prepare them.    --Goldsmith.
      [1913 Webster]

   3. (Logic) An affirmation, or distinction from a supposition
      or hypothesis.
      [1913 Webster]

   4. (Mus.) The accented part of the measure, expressed by the
      downward beat; -- the opposite of arsis.
      [1913 Webster]

   5. (Pros.)
      (a) The depression of the voice in pronouncing the
          syllables of a word.
      (b) The part of the foot upon which such a depression
          falls.
          [1913 Webster]