Old European's bitterness voiced (4)
I believe the answer is:
gaul
'old european's' is the definition.
'Gaul' can be an answer for 'european's' (Gaul is an example). I am not sure about the 'old' bit.
'bitterness voiced' is the wordplay.
'bitterness' becomes 'gall' (synonyms).
'voiced' shows a homophone (sound like).
'gall' is a homophone of 'GAUL'.
Can you help me to learn more?
(Other definitions for gaul that I've seen before include "Asterix, for example" , "Ancient region of France/Belgium in Caesar's time" , "old country" , "Ancient area of western Europe" , "Caesar's name for old France" .)