Toy with no head found in sack (5)
I believe the answer is:
rifle
'sack' is the definition.
(thesaurus)
'toy with no head' is the wordplay.
'toy' becomes 'trifle' (I've seen this before).
'with no head' means to remove the first letter.
'trifle' with its initial letter removed is 'RIFLE'.
'found in' acts as a link.
(Other definitions for rifle that I've seen before include "disarray" , "Go through in search" , "Steal and carry off - firearm" , "An arm" , "lock, stock and barrel" .)