Second quality jam (6)
I believe the answer is:
strait
'jam' is the definition.
(thesaurus)
'second quality' is the wordplay.
'second' becomes 's' (common abbreviation).
'quality' becomes 'trait' (I've seen this before).
's'+'trait'='STRAIT'
(Other definitions for strait that I've seen before include "Narrow sea passage" , "Narrow channel of the sea joining two larger bodies of water" , "of Gibraltar, for example" , "Catch in a trap" , "Difficulty - strict" .)