Herdsmen heading off for sources of water (6)
I believe the answer is:
rivers
'herdsmen' is the definition.
Although both the answer and definition are plural nouns, I cannot see how they can define each other.
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for rivers that I've seen before include "''Only Our ... Run Free'' (MacConnell ballad)" , "Comedienne Joan" , "Thames and Hudson?" , "''Only Our ... Run Free'' (McConnell ballad)" , "Large natural streams of water" .)