Something supposedly lucky that's on the hoof? (9)
I believe the answer is:
horseshoe
'something supposedly lucky' is the definition.
I can't judge whether this defines the answer.
'that's on the hoof?' is the wordplay.
'that's' becomes 'hoe' (I can't explain this - if you can you should give a lot more credence to this answer).
'on' is a charade indicator (letters next to each other).
'the hoof?' becomes 'horses' (horse's hoof is a kind of hoof).
'hoe' put after 'horses' is 'HORSESHOE'.
Can you help me to learn more?
(Other definitions for horseshoe that I've seen before include "Plate nailed to equine hoof" , "seen at extremities of bay" , "Lucky thing" , "Steed's footwear" , "Bat" .)