Trouble involving Republican poet’s fellowship (11)
I believe the answer is:
brotherhood
'fellowship' is the definition.
(thesaurus)
'trouble involving republican poet's' is the wordplay.
'trouble' becomes 'bother' (synonyms).
'involving' means one lot of letters goes inside another.
'republican' becomes 'R' (abbreviation).
'poet' becomes 'hood' (Thomas Hood, b799-b8he).
'bother' enclosing 'r' is 'brother'.
'brother'+'hood'='BROTHERHOOD'
(Other definitions for brotherhood that I've seen before include "association" , "Fraternity" , "Feeling of close kinship" , "union" , "Community" .)