Uncle Pat, a merry entertaining old fruit (10)
I believe the answer is:
cantaloupe
'fruit' is the definition.
(I know that cantaloupe is a fruit)
'uncle pat a merry entertaining old' is the wordplay.
'merry' is an anagram indicator (merry can mean drunk).
'entertaining' is an insertion indicator (inviting in, as for dinner).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'uncle'+'pat'+'a'='unclepata'
'unclepata' is an anagram of 'cantalupe'.
'cantalupe' going around 'o' is 'CANTALOUPE'.
(Other definitions for cantaloupe that I've seen before include "Musk-melon" , "Small melon with ribbed skin" , "Small melon variety" , "musk melon" , "Type of melon" .)