Fruit is round, as it happens (5)
I believe the answer is:
olive
'fruit' is the definition.
(I know that olive is a type of fruit)
'round as it happens' is the wordplay.
'round' becomes 'o' (o is a circular letter).
'as it happens' becomes 'live' (as in live television).
'o'+'live'='OLIVE'
'is' acts as a link.
(Other definitions for olive that I've seen before include "Evergreen Mediterranean tree" , "A Med. fruit" , "Green shade; its branch for peace" , "Greyish-green colour" , "Yellow-green colour like Mediterranean fruit" .)