Peg trembled without a top (4)
I believe the answer is:
hook
'peg' is the definition.
(I've seen this before)
'trembled without a top' is the wordplay.
'trembled' becomes 'shook' (shake can mean to tremble).
'without a top' means to remove the first letter (in a down clue, top can mean the top letter).
'shook' with its first letter removed is 'HOOK'.
(Other definitions for hook that I've seen before include "Piece of bent material to suspend, catch fish etc" , "Bag" , "Punch; fish catcher" , "By . . . . or by crook - whatever it takes" , "Legendary captain" .)