Exclusive small pen (5)
I believe the answer is:
scoop
'exclusive' is the definition.
('scoop' can be a synonym of 'exclusive')
'small pen' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'pen' becomes 'coop' (I've seen this before).
's'+'coop'='SCOOP'
(Other definitions for scoop that I've seen before include "Exclusive report" , "Dig out - story that makes the headlines" , "Exclusive news story" , "Kind of ladle or shovel-like tool - reporters seek it" , "Exclusive newspaper story" .)