What a marvel - got victory over backward Communist (6)
I believe the answer is:
wonder
'what a marvel' is the definition.
(synonyms)
'victory over backward communist' is the wordplay.
'victory' becomes 'won' (I've seen this before).
'over' means one lot of letters go next to another.
'backward' says the letters should be written in reverse.
'communist' becomes 'red' (red can informally mean communist).
'red' reversed gives 'der'.
'won'+'der'='WONDER'
'got' is the link.
(Other definitions for wonder that I've seen before include "Something amazing" , "Scene of Alice's adventures" , "Feeling of surprise and admiration" , "Ponder" , "Transmitted; despatched" .)