Bishop not at home in session (4)
I believe the answer is:
bout
'session' is the definition.
(thesaurus)
'bishop not at home' is the wordplay.
'bishop' becomes 'b' (abbreviation used in chess).
'not at home' becomes 'out' (I've seen this before).
'b'+'out'='BOUT'
'in' acts as a link.
(Other definitions for bout that I've seen before include "(Drinking) session" , "Short period of intense activity" , "Period of illness or boxing match" , "Wrestling contest" , "Attack (of illness)" .)