Former Greek monetary unit (7)
I believe the answer is:
drachma
'former greek monetary unit' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for drachma that I've seen before include "Old Greek settler" , "Formerly the basic unit of money in Greece" , "Money no longer available" , "Former Greek currency unit" , "European currency replaced by the euro in 2002" .)