why is ‘fruit’ referred to as 水果 if 果 already means fruit?
droooze wrote:


  果 does not only mean fruit - it can mean "result, accomplishment, achievement" as well. 


It is a good explanation for why we don't just say 果  when we mean 'fruit'. 

Also, 腰果, 白果 are nut (果仁). The single character 果 is too general to be used specifically for 'fruit'.

And there's more:

生果唔同水果 

For Cantonese, 生果 and 水果 are two different things. 生果 is fruit that grown on tree and 水果 is edible plant that grow in water (e.g. 水蓮藕 is a kind of root and 水菱角 is kind of nut). But for Mandarin, 水果 referred to all fruit that grow on tree and the term 生果 is rarely used.