Big round pickle, alternatively (5)
I believe the answer is:
major
'big' is the definition.
(I've seen this before)
'round pickle alternatively' is the wordplay.
'round' shows that the letters should be reversed in order.
'pickle' becomes 'jam' (both can mean a problem or difficulty).
'alternatively' becomes 'or'.
'jam' back-to-front is 'maj'.
'maj'+'or'='MAJOR'
(Other definitions for major that I've seen before include "Uppermost" , "Commissioned military officer" , "Bigger" , "Important; rank" , "Significant; rank" .)