Certain drunken celeb's a pain (11)
I believe the answer is:
inescapable
'certain' is the definition.
('inescapable' can be a synonym of 'certain')
'drunken celeb's a pain' is the wordplay.
'drunken' indicates an anagram.
'celebs'+'a'+'pain'='celebsapain'
'celebsapain' is an anagram of 'INESCAPABLE'.
(Other definitions for inescapable that I've seen before include "It cannot be denied" , "it's unlikely to be denied" , "Not possible to avoid" , "Perhaps ubiquitous" , "Not to be avoided" .)