Part of terrain was heavy accompaniment to run-off (8)

I believe the answer is:

rainwash

I'm a little stuck... Click here to teach me more about this clue!

'run-off' is the definition.
I don't know anything about this answer so I can't judge whether this works.

'part of terrain was heavy accompaniment' is the wordplay.
'part of' says the answer is hidden in the clue.
'RAINWASH' can be found hidden inside 'terrain was heavy accompaniment'.

'to' acts as a link.

Can you help me to learn more?

I've seen this clue in The Independent.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.

Connecting...