The way to take unusually keen interest (10)
I believe the answer is:
usuriously
'the way to take unusually keen interest' is the definition.
I can't tell whether this defines the answer.
'the way to take' is the wordplay.
I cannot quite see how this works, but
'way' could be 's' (Compass direction - South) and 's' is present in the answer.
'take' could be 'r' (abbreviation for 'recipe', Latin for 'take') and 'r' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Another definition for usuriously that I've seen is " How money is lent at extortionate interest rates".)