Wedge (3)
'wedge' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for jam that I've seen before include "Sweet stuff for bread - stuff it in" , "Fruit preserve" , "Block signals" , "awful traffic" , "Spread; improvise (jazz)" .)
'wedge' is the definition.
(I know that shim is a type of wedge)
This is all the clue.
(Other definitions for shim that I've seen before include "Thin spacer" , "Thin strip of metal" , "sort of rod used in reactors" , "Slip" .)