Europe sometimes requires this currency (4)
I believe the answer is:
peso
'this currency' is the definition.
(I have seen 'Mexican currency' mean 'peso' so perhaps 'currency' could also mean 'peso')
'europe sometimes' is the wordplay.
'PESO' is hidden within the letters.
However, I am not sure how the hidden word is indicated.
'requires' acts as a link.
Can you help me to learn more?
(Other definitions for peso that I've seen before include "Currency of Mexico" , "Mexican monetary unit" , "Mexican currency unit" , "Foreign currency" , "Unit of Mexican money" .)