Baltic supplier seen in moderation (4)
I believe the answer is:
oder
'baltic supplier' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'in moderation' is the wordplay.
'in' indicates a hidden word.
'ODER' is hidden within 'moderation'.
'seen' is the link.
Can you help me to learn more?
(Other definitions for oder that I've seen before include "European flower" , "East European river" , "Rode around the European river" , "School blazer insignia" , "River that, with the Neisse, forms the German-Polish border" .)