Crossword Genius

From prison, dash to the open ground (8)

Ross

I believe the answer is:

dartmoor

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

'from prison' is the definition.
I can't judge whether this defines the answer.

'dash to the open ground' is the wordplay.
'dash' becomes 'd'art' (synonyms).
'to the open ground' becomes 'moor' (I've seen this before).
'dart'+'moor'='DARTMOOR'

Can you help me to learn more?

(Other definitions for dartmoor that I've seen before include "Famous English prison in Devon" , "Devon pony breed" , "National Park in Devon" , "with ponies?" , "West Country prison" .)

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