Dodgy sort of bag with no opening (4)
I believe the answer is:
iffy
'dodgy' is the definition.
(I've seen this before)
'sort of bag with no opening' is the wordplay.
'sort of bag' becomes 'jiffy' (Jiffy bag is a type of envelope or bag).
'with no opening' means to remove the first letter.
'jiffy' with its initial letter taken away is 'IFFY'.
(Other definitions for iffy that I've seen before include "Unsure" , "Dodgy" , "Doubtful (colloq.)" , "Questionable (inf)" , "Questionable - uncertain" .)