Stone in fruit, large (5)
I believe the answer is:
pearl
'stone' is the definition.
(I have seen 'precious stone' mean 'pearl' so perhaps 'stone' could also mean 'pearl')
'fruit large' is the wordplay.
'fruit' becomes 'pear' (pear is a kind of fruit).
'large' becomes 'L' (eg in clothes sizes).
'pear'+'l'='PEARL'
'in' acts as a link.
(Other definitions for pearl that I've seen before include "Lustrous globule prized as a gem" , "Gem; size of type" , "Highly-valued thing" , "Precious stone from shellfish" , "Precious gem" .)