River craft east of delta (4)
I believe the answer is:
dart
'river' is the definition.
(River Dart in Devon)
'craft east of delta' is the wordplay.
'craft' becomes 'art' (both can mean cunning or trickery).
'east of' means one lot of letters go next to another (some letters go to the right of others).
'delta' becomes 'd' (phonetic alphabet: alpha, bravo, charlie etc.).
'art' after 'd' is 'DART'.
(Other definitions for dart that I've seen before include "one destined to go on board?" , "Tuck; arrow" , "Devon river - bound - race" , "Fish < from River" , "One fired" .)