Feel-good chemical to stop open transformation (9)
I believe the answer is:
endorphin
'open transformation' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'feel-good chemical to stop' is the wordplay.
I cannot really see how this works, but
'stop' could be 'end' (synonyms) and 'end' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for endorphin that I've seen before include "Hormone in the brain with an analgesic effect" , "Neurochemical with analgesic properties - dinner hop (anag)" , "Opiate-like substance produced in the brain" , "painkiller" .)