Knight, despicable type, turned back river (6)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
tigris
'river' is the definition.
(I know that Tigris is a river)
'knight despicable type turned back' is the wordplay.
'knight' becomes 'sir' (a knight has the title Sir).
'despicable type' becomes 'git' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'turned back' is a reversal indicator.
'sir'+'git'='sirgit'
'sirgit' in reverse letter order is 'TIGRIS'.
Can you help me to learn more?
(Other definitions for tigris that I've seen before include "Flower of Baghdad" , "Great river flowing from Turkey through Iraq" , "Baghdad's river" , "Great river of 30 across" , "Major tributary of the Euphrates" .)