English river split after junction (5)
I believe the answer is:
trent
'english river' is the definition.
(River Trent in England)
'split after junction' is the wordplay.
'split' becomes 'rent' (synonyms).
'after' means one lot of letters go next to another.
'junction' becomes 't'.
'rent' put after 't' is 'TRENT'.
(Other definitions for trent that I've seen before include "Main river of the Midlands" , "Nottingham's river" , "River at Newark/Stoke" , "Little Nell family; Eng. river" , "Crossword frame" .)