Hateful gin has one turning to rum in the morning (7)
I believe the answer is:
goddamn
'hateful' is the definition.
Both the answer and definition are adjectives. Perhaps you can see an association between them that I can't see?
'gin has one turning to rum in the morning' is the wordplay.
I cannot really see how this works, but
'one' could be 'odd' (I've seen this before) and 'odd' is present in the answer.
'morning' could be 'am' (as in 12:00 AM) and 'am' is present 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 goddamn that I've seen before include "Blasted - odd G-man (anag)" , "expletive" .)