Becoming standard finally, European coin (6)
I believe the answer is:
decent
'becoming' is the definition.
(synonyms)
'standard finally european coin' is the wordplay.
'finally' suggests the final letters.
'european' becomes 'E' (abbreviation e.g. EU).
'coin' becomes 'cent' (cent is a kind of coin).
The last letter of 'standard' is 'd'.
'd'+'e'+'cent'='DECENT'
(Other definitions for decent that I've seen before include "Honourable or modest" , "Generally acceptable" , "Generous and modestly clothed" , "Modest and respectable" , "Morally respectable" .)