One hundredth of a euro (4)
I believe the answer is:
cent
'one hundredth of a euro' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for cent that I've seen before include "One-hundredth of the value of the basic unit" , "One-hundredth of the basic monetary unit" , "1/100 of various currencies" , "One hundredth of a euro" , "Fractional monetary unit" .)