The fruits of oranges, lemons and other citrus are a special kind of berry called a hesperidium. Of course the botanical definition of a berry, as opposed to the gardeners’ definition, throws up some interesting anomalies. The botanical definition of a berry is a fleshy fruit resulting from one ovary with one or more seeds and, usually, a thin skin. So although strawberries and raspberries are not berries, bananas, cucumbers, currants, aubergines, tomatoes and grapes are berries! The good news is that gooseberries are berries.
Oranges are berries but because the skins are thickened and the juice is contained in special, thickened hairs called vesicles, they have their own name and are accurately called hesperidiums (or maybe hesperidia?).
I think the name comes from hesperides which is a word from Greek mythology. The Hesperides were the ‘nymphs of the evening’ and named, in turn for hesperos, meaning evening (vesper in Latin).
The Garden of Hesperides was Hera’s orchard (Hera was the goddess of Marriage) located in the west (where the sun set – an evening theme is developing – and now thought to be modern-day Portugal). This is where a tree (or orchard) of trees grew that produced golden apples. When eaten, these bestowed immortality. There seems, to me, a link with Bible stories here.
It is very likely that these golden apples were in fact oranges, even though these are originally from China. But if the terracotta army in China was really made by Greeks the whole thing ties up quite nicely.