Extra extra in addition (8)
I believe the answer is:
moreover
'in addition' is the definition.
('moreover' can be a synonym of 'in addition')
'extra extra' is the wordplay.
'extra' becomes 'more' (I've seen this before).
'extra' becomes 'over'.
'more'+'over'='MOREOVER'
(Other definitions for moreover that I've seen before include "Furthermore, in addition" , "Besides, in addition" , "as well" .)