The Collaborative International Dictionary of English v.0.48:

Tripos \Tri"pos\, n.; pl. Triposes. [Gr. ? a tripod. See
   Tripod.]
   1. A tripod. [Obs.] --Dryden.
      [1913 Webster]

   2. A university examination of questionists, for honors;
      also, a tripos paper; one who prepares a tripos paper.
      [Cambridge University, Eng.]
      [1913 Webster]

   Classical tripos examination, the final university
      examination for classical honors, optional to all who have
      taken the mathematical honors. --C. A. Bristed.

   Tripos paper, a printed list of the successful candidates
      for mathematical honors, accompanied by a piece in Latin
      verse. There are two of these, designed to commemorate the
      two tripos days. The first contains the names of the
      wranglers and senior optimes, and the second the names of
      the junior optimes. The word tripos is supposed to refer
      to the three-legged stool formerly used at the
      examinations for these honors, though some derive it from
      the three brackets formerly printed on the back of the
      paper. --C. A. Bristed.
      [1913 Webster]

WordNet (r) 3.0 (2006):

tripos
    n 1: final honors degree examinations at Cambridge University