When the interest rate's one pound? (5)
I believe the answer is:
april
'when the interest rate's' is the definition.
I can't tell whether this defines the answer.
'one pound?' is the wordplay.
'one' becomes 'apri' (I can't explain this - if you can you should give a lot more credence to this answer).
'pound?' becomes 'L' (the pound sign is based on an L).
'apri'+'l'='APRIL'
Can you help me to learn more?
(Other definitions for april that I've seen before include "Part of spring" , "March is followed by this" , "Fourth month" , "Springtime rain" , "''... is the cruellest month''(Elliot)" .)