British poet remaining inside association (11)
I believe the answer is:
brotherhood
'association' is the definition.
(thesaurus)
'british poet remaining inside' is the wordplay.
'british' becomes 'br'.
'poet' becomes 'hood' (I've seen this in other clues**).
'remaining' becomes 'other' ('other' can be similar in meaning to 'remaining').
'inside' indicates putting letters inside.
'br'+'hood'='brhood'
'brhood' placed around 'other' is 'BROTHERHOOD'.
(Other definitions for brotherhood that I've seen before include "Fraternity" , "Community" , "Feeling of close kinship" , "association" , "union" .)