Advanced degree? (3)
'advanced degree' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for phd that I've seen before include "Highest university degree" , "Letters denoting holder of university doctorate" , "Initially a top university degree" , "In brief, top university qualification" .)
(Other definitions for nth that I've seen before include "Umpteenth" , "To the -- degree" .)
(Another definition for mba that I've seen is " Higher business degree".)