Fruit -- round variety (6)
I believe the answer is:
'fruit' is the definition.
(orange is a kind of fruit)
'round variety' is the wordplay.
'round' becomes 'o' (round can mean a round object).
'variety' becomes 'range' (I've seen this before).
(Other definitions for orange that I've seen before include "African flower" , "Loyalist colour" , "Colour of Northern Ireland unionism" , "One's pipped" , "Mandarin?" .)