Round bag (5)
I believe the answer is:
catch
This clue is a double definition.
'round' is the first definition.
(catch is a type of musical round or song)
'bag' is the second definition.
(synonyms)
(Other definitions for catch that I've seen before include "Hidden problem; trap" , "problem being concealed" , "It's taken by a fielder to dismiss a player in baseball and cricket" , "Dismiss (batsman); break (in voice)" , "secure" .)