Tory pamphlet editor shortened (10)
I believe the answer is:
contracted
'shortened' is the definition.
('contract' can be a synonym of 'shorten')
'tory pamphlet editor' is the wordplay.
'tory' becomes 'con' (abbreviation for Conservative).
'pamphlet' becomes 'tract' ('tract' can be a synonym of 'pamphlet').
'editor' becomes 'ed'.
'con'+'tract'+'ed'='CONTRACTED'
(Other definitions for contracted that I've seen before include "Formally agreed; shrank" , "Got shorter" .)