Fruit — old cookers (7)
I believe the answer is:
oranges
'fruit' is the definition.
(oranges are a type of fruit)
'old cookers' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'cookers' becomes 'ranges' (I can't explain this - if you can you should believe this answer much more).
'o'+'ranges'='ORANGES'
Can you help me to learn more?
(Other definitions for oranges that I've seen before include "Go snare these fruits" , "a zesty lot" , "Navel, blood and Seville are all varieties of these" , "'Mandarins, say (7)'" , "Mandarins, satsumas etc." .)