Don't have any main course? (5)
I believe the answer is:
drift
'course?' is the definition.
(thesaurus)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for drift that I've seen before include "Move casually or aimlessly" , "Stray" , "Coast" , "Snow heaped up by wind" , "Move with the current" .)