Defeated front line left mostly separated (10)

I believe the answer is:

vanquished

I'm a little stuck... Click here to teach me more about this clue!

'defeated' is the definition.
(similar in meaning)

'front line left mostly separated' is the wordplay.
I cannot quite understand how this works, but
'front' could be 'van' (I've seen this in another clue) and 'van' is found within the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?

(Other definitions for vanquished that I've seen before include "Squid haven (anag.)" , "Defeated" .)

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

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