ripe fruit; mellow fruit
A noun phrase describing fruit that has fully ripened, often with a nuance of softness and sweetness. Used literally and sometimes figuratively for something that has reached its peak.
I picked and ate the ripe fruit from the garden.
Her singing voice is as rich as mellow fruit.
A straightforward compound of 熟れた (ureta, 'ripened') and 果実 (kajitsu, 'fruit'). No special historical derivation.