Obscure European coin worth ten cents (4)
I believe the answer is:
dime
'coin worth ten cents' is the definition.
(US ten cent coin)
'obscure european' is the wordplay.
'obscure' becomes 'dim' (both can mean dark).
'european' becomes 'E' (abbreviation e.g. EU).
'dim'+'e'='DIME'
(Other definitions for dime that I've seen before include "US 10 cent coin" , "10 US cents" , "Ten-cent coin in America" , "Something round and silvery" , "Ten cents in USA" .)