One down to get a bit of jewellery? (5,5)
I believe the answer is:
pearl diver
'bit of jewellery?' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'one down to get a' is the wordplay.
I cannot really understand how this works, but
'one' could be 'i' (Roman numeral) and 'i' is present in the answer.
'down' could be 'd' and 'd' is present in the answer.
'a' is within the answer.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for pearl diver that I've seen before include "One who seeks gems underwater" , "Oystercatcher" , "Seeker of gems" , "one takes a deep breath" .)