Putting one's head in this may make one so wretched (5)
I believe the answer is:
noose
'putting one's head in this may make one so wretched' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'in this may make one so wretched' is the wordplay.
'in' indicates putting letters inside.
'this may make' indicates anagramming the letters.
'wretched' indicates an anagram.
'one' with letters rearranged gives 'noe'.
'so' is an anagram of 'os'.
'noe' going around 'os' is 'NOOSE'.
Can you help me to learn more?
(Other definitions for noose that I've seen before include "Loop in a rope made with a slip knot" , "Hangman's equipment" , "Loop formed by means of a slip knot" , "Loop with running knot" , "Halter loop" .)