The main fight (3,6)

I believe the answer is:

sea battle

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'the' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'main fight' is the wordplay.
'main' becomes 'sea' (synonyms).
'fight' becomes 'battle' (synonyms).
'sea'+'battle'='SEA BATTLE'

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