Romeo in trouble with companion (7)
I believe the answer is:
brother
'companion' is the definition.
(thesaurus)
'romeo in trouble' is the wordplay.
'romeo' becomes 'r' (phonetic alphabet: alpha, bravo, charlie etc.).
'in' means one lot of letters goes inside another.
'trouble' becomes 'bother' (synonyms).
'r' put within 'bother' is 'BROTHER'.
'with' is the link.
(Other definitions for brother that I've seen before include "Male sibling" , "Fellow-member" , "Relation" , "Trade unionist" , "Eg, monk, friar" .)