Somebody that's eaten one midsummer fruit (9)
I believe the answer is:
persimmon
'fruit' is the definition.
(persimmon is a kind of fruit)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for persimmon that I've seen before include "Edible fruit" , "Tropical fruit" , "Orange fruit resembling a plum - miner's mop (anag)" .)