Keep tearing around endlessly (6)

I believe the answer is:

retain

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'keep tearing' is the definition.
'retain' can be an answer for 'keep' (synonyms). I am not sure about the 'tearing' bit.

'around endlessly' is the wordplay.
'around' becomes 're' (regarding).
'endlessly' becomes 'tain' (I can't justify this - if you can you should give a lot more credence to this answer).
're'+'tain'='RETAIN'

Can you help me to learn more?

(Other definitions for retain that I've seen before include "Keep, hold on to something" , "Hold in position" , "'Hold, keep back (6)'" , "Hire - keep" , "Continue to hold on to" .)

I've seen this clue in the Evening Standard.

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