Runs across gatherings of horses and hounds (5)
I believe the answer is:
meets
'runs across' is the definition.
('meet' can be a synonym of 'run across')
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for meets that I've seen before include "Comes into the presence of" , "Hunts" , "Gathers together" , "Joins with" , "Encounters or suffices" .)