Brit fish, mostly ordinary (5)

I believe the answer is:

anglo

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This might be a double definition.

'brit fish' is the first definition.
The definition suggests a singular noun which matches the answer.

'mostly ordinary' is the second definition.
The definition suggests a singular noun which matches the answer.

Can you help me to learn more?

(Other definitions for anglo that I've seen before include "Prefix meaning English or British" , "Prefix denoting English" .)

I've seen this clue in The Times and The Sunday Times.

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