Big jar picked up (5)
I believe the answer is:
great
'big' is the definition.
(I know that big can be written as great)
'jar picked up' is the wordplay.
'jar' becomes 'grate' (make unpleasant sound).
'picked up' indicates a 'sounds like' (homophone) clue.
'grate' is a homophone of 'GREAT'.
(Other definitions for great that I've seen before include "Large; fine" , "cracking" , "Important; immense" , "Enormous" , "and 12 Down: Powerful dog" .)