Second newspaper to exclude supplement (7)
I believe the answer is:
sidebar
'supplement' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.
'second newspaper to exclude' is the wordplay.
'second' becomes 's' (common abbreviation).
'newspaper' becomes 'i' (the i is a British newspaper).
'to exclude' becomes 'debar' (synonyms).
's'+'i'+'debar'='SIDEBAR'
Can you help me to learn more?
(Other definitions for sidebar that I've seen before include "Short item throwing light on the main article - braised (anag)" , "South African solicitors" , "Explanatory panel" , "Courtroom conference between the lawyers and the judge" .)