It stops Hank having an unsuccessful winter (6)
I believe the answer is:
halter
'it stops hank having an unsuccessful winter' is the definition.
The definition suggests a singular noun which matches the answer.
'it' is the wordplay.
I cannot quite understand how this works, but
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is present in the answer.
The remaining letters 'haler' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for halter that I've seen before include "Rope for leading animals" , "Tether" , "Horse's lead" , "Rope or leather strap for tying up horse" , "Rope or canvas on a horse's head" .)