Definition of "tripos"

Thales sent the golden tripos, which the fishermen found and the oracle commanded to be “given to the wisest”, to Bias, Bias to Solon, etc.

1624, Democritus Junior [pseudonym; Robert Burton], The Anatomy of Melancholy: […], 2nd edition, Oxford, Oxfordshire: Printed by John Lichfield and James Short, for Henry Cripps

Scarce had I said, He shook the holy Ground: / The Lawrels, and the lofty Hills around: / And from the Tripos rush'd a bellowing sound.

1697 [19 BCE], John Dryden, The Third Book of the Æneis, translation of Aeneid by Virgil, lines 122–124; republished in The Works of John Dryden, volume 5, University of California Press, 1988, page 421

I'm seriously thinking of chucking my tripos and taking up the History Special.

1891, Rudolph Chambers Lehmann, Harry Fludyer at Cambridge, page 9

It's time you thought. The Tripos is the beginning of life, not the end. In less than two years you will have got your B.A. What are you going to do with it?

1907, E.M. Forster, The Longest Journey, Part I, I [Uniform ed., p. 20]