Horse taking good man over rising river (5)
I believe the answer is:
steed
'horse' is the definition.
(I know that horse can be written as steed)
'good man over rising river' is the wordplay.
'good man' becomes 'st' (abbreviation for saint).
'over' says to put letters next to each other.
'rising' says the letters should be written in reverse (going up in a down clue).
'river' becomes 'dee' (River Dee).
'dee' in reverse letter order is 'eed'.
'st'+'eed'='STEED'
'taking' acts as a link.
(Other definitions for steed that I've seen before include "Spirited horse" , "Powerful horse" , "Stallion" , "Horse, mount" , "(Poetic) horse" .)