Granny in the thrall of Botswanan naturist (5)

I believe the answer is:

nanna

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'granny in the thrall' is the definition.
'nanna' can be an answer for 'granny' (I've seen this in another clue). I'm not certain of the 'in the thrall' bit.

'of botswanan naturist' is the wordplay.
'of' indicates the answer is hidden within the clue.
'NANNA' is hidden within 'botswanan naturist'.

Can you help me to learn more?

(Other definitions for nanna that I've seen before include "Gran" , "Mother's mother?" , "old Indian currency" , "granny" , "Grandma" .)

I've seen this clue in The Independent.

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