Ring in the nose as a halter (5)
I believe the answer is:
noose
'a halter' is the definition.
(I've seen this before)
'ring in the nose' is the wordplay.
'ring' becomes 'o' (O is the shape of a ring).
'in' means one lot of letters goes inside another.
'o' put inside 'nose' is 'NOOSE'.
'as' is the link.
(Other definitions for noose that I've seen before include "Ring of rope" , "Hangman's rope" , "it could endanger your life" , "trap" , "Catcher" .)