One who won't give up row over river (5)
I believe the answer is:
trier
'one who won't give up' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'row over river' is the wordplay.
'row' becomes 'tier' (a tier is a row of things).
'over' is an insertion indicator.
'river' becomes 'r' (abbreviation for river).
'tier' going around 'r' is 'TRIER'.
Can you help me to learn more?
(Other definitions for trier that I've seen before include "One persevering" , "place in Germany" , "One who perseveres" , "Test" , "town in Germany" .)