Fourth, twenty-fourth and twenty-fifth letters, all going to the third, reportedly? (6)
I believe the answer is:
rivers
'twenty-fourth and twenty-fifth letters all going to the third reportedly?' is the definition.
I can't judge whether this definition defines the answer.
'fourth' is the wordplay.
I cannot quite see how this works, but
'fourth' could be 'iv' and 'iv' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for rivers that I've seen before include "Large natural streams of water" , "''Only Our ... Run Free'' (MacConnell ballad)" , "Comedienne Joan" , "''Only Our ... Run Free'' (McConnell ballad)" , "Thames and Hudson?" .)