Hangman’s halter (5)
I believe the answer is:
noose
'hangman's halter' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for noose that I've seen before include "Loop for catching animals" , "form of punishment" , "Loop in a lariat" , "Hangman's or cowboy's loop" , "Loop of rope with a slipknot" .)