Weight of a peach, perhaps? (5)

I believe the answer is:
stone
'weight' is the definition.
(stone is a unit of weight)
'a peach perhaps?' is the wordplay.
I cannot quite see how this works, but
'a' could be 'one' and 'one' is found within the answer.
The remaining letters 'st' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'of' acts as a link.
Can you help me to learn more?
(Other definitions for stone that I've seen before include "diamond, say" , "Imperial unit of weight" , "Kernel" , "Hard lump of mineral matter" , "Olive pip" .)
