Witch for strangling knight put to death (4)
I believe the answer is:
hang
'put to death' is the definition.
(hanging is a kind of putting to death)
'witch for strangling knight' is the wordplay.
'witch' becomes 'hag' (synonyms).
'for strangling' is an insertion indicator (inserted letters are held or 'strangled').
'knight' becomes 'N' (chess abbreviation).
'hag' placed around 'n' is 'HANG'.
(Other definitions for hang that I've seen before include "Hover" , "Be suspended" , "Apply most severe sanction" , "Go to the gallows" , "Suspend, perhaps execute" .)