Free the 'orse outside (8)

I believe the answer is:

untether

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'free the 'orse outside' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.

'free the 'orse outside' is the wordplay.
'free' indicates anagramming the letters.
''orse' becomes ''unter' ('hunter' - I've seen this before - said with the 'H' dropped, a cockney accent, like 'horse' was).
'outside' indicates putting letters inside.
'the' anagrammed gives 'eth'.
'eth' going inside 'unter' is 'UNTETHER'.

Can you help me to learn more?

(Other definitions for untether that I've seen before include "Release (tied animal)" , "Set free" .)

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