The Collaborative International Dictionary of English v.0.48:
Double first \Dou"ble first`\ (Eng. Universities) (a) A degree of the first class both in classics and mathematics. (b) One who gains at examinations the highest honor both in the classics and the mathematics. --Beaconsfield. [1913 Webster]WordNet (r) 3.0 (2006):
double first n 1: a first-class honours degree in two subjects