Leave one of the later courses, by the sound of it (6)
I believe the answer is:
desert
'leave' is the definition.
(desert can mean to leave or abandon)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for desert that I've seen before include "See 1" , "Waterless area of land" , "Defect, forsake" , "See 23" , "Sahara, Gobi, etc" .)