In extremes of penury, a loan means a lot (6)
I believe the answer is:
plenty
'a lot' is the definition.
(I've seen this in another clue)
'in extremes of penury a loan' is the wordplay.
'in' indicates putting letters inside.
'extremes of' suggests removing the centre (only the letters at the extremes of the word).
'a loan' becomes 'lent' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'penury' with its centre taken out is 'py'.
'py' going around 'lent' is 'PLENTY'.
'means' is the link.
Can you help me to learn more?
(Other definitions for plenty that I've seen before include "Amplitude or abundance" , "Masses" , "A full supply - lots" , "Copiousness" , "As much as necessary" .)