Fruit expert on the Tube? (7)
I believe the answer is:
product
'fruit' is the definition.
(thesaurus)
'expert on the tube?' is the wordplay.
'expert' becomes 'pro' (short for professional).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'the tube?' becomes 'duct' (type of tube or canal).
'pro'+'duct'='PRODUCT'
(Other definitions for product that I've seen before include "Drop cut (anag.)" , "Manufactured article for sale" , "Commodity offered for sale" , "See 5" , "Result of multiplication" .)