Dull friend reaches impasse (9)
I believe the answer is:
stalemate
'impasse' is the definition.
('stalemate' can be a synonym of 'impasse')
'dull friend' is the wordplay.
'dull' becomes 'stale'.
'friend' becomes 'mate' (mate is a kind of friend).
'stale'+'mate'='STALEMATE'
'reaches' acts as a link.
(Other definitions for stalemate that I've seen before include "Chess game deadlock" , "situation without a winner" , "A no-win situation in chess" , "Situation offering no way forward" , "Inconclusive result" .)