Ground rent at high level? (8)

I believe the answer is:

crevasse

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'ground rent' is the definition.
'crevasse' can be an answer for 'rent' (thesaurus). I'm not sure about the 'ground' bit.

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for crevasse that I've seen before include "opening" , "big split" , "Deep glacial fissure" , "climbing hazard in glacier" , "Deep glacial crack" .)

I've seen this clue in The Sun and The Globe and Mail.

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