The Collaborative International Dictionary
Double first
Double first \Dou"ble first`\ (Eng. Universities)
A degree of the first class both in classics and mathematics.
One who gains at examinations the highest honor both in the classics and the mathematics.
--Beaconsfield.
Wiktionary
double first
n. 1 (context UK English) A first-class degree both in classics and mathematics. 2 (context UK English) One who achieves such a degree.
WordNet
double first
n. a first-class honours degree in two subjects