Mint coin, sovereign maybe (10)

I believe the answer is:

pennyroyal

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'mint' is the definition.
(I know that pennyroyal is a type of mint)

'coin sovereign maybe' is the wordplay.
'coin' becomes 'penny' (penny is a kind of coin).
'sovereign maybe' becomes 'royal' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'penny'+'royal'='PENNYROYAL'

Can you help me to learn more?

(Other definitions for pennyroyal that I've seen before include "Small plant of mint family" , "medicinal plant" , "Plant used in herbal medicine (part of the queen's shilling?)" .)

I've seen this clue in The Telegraph.

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