Ruler has a piece of fruit (7)
I believe the answer is:
sultana
'fruit' is the definition.
(sultana is a kind of fruit)
'ruler has a piece' is the wordplay.
I cannot really see how this works, but
'ruler' could be 'sultan' (sultan is a kind of ruler) and 'sultan' is present in the answer.
'a' is within the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'of' acts as a link.
Can you help me to learn more?
(Other definitions for sultana that I've seen before include "Wife of an Eastern potentate" , "A bit of a fruitcake" , "Sovereign's mother perhaps" , "mistress abroad" , "Dried fruit - Muslim ruler's consort" .)