Medium to large piece of fruit (6)
I believe the answer is:
medlar
'fruit' is the definition.
(apple-like fruit)
'medium to large piece' is the wordplay.
I cannot quite understand how this works, but
'medium' could be 'm' (as in UK clothing sizes) and 'm' is present in the answer.
'large' could be 'l' (eg in clothes sizes) and 'l' is found in the answer.
'piece' could be 'r' (abbreviation for Rook) and 'r' is found in the answer.
This explanation may well be incorrect...
'of' is the link.
Can you help me to learn more?
(Other definitions for medlar that I've seen before include "Dermal (anag.)" , "Apple-like fruit" , "Led ram (anag) - fruit related to the apple" , "Red Mal turns to the fruit tree" .)