Kept guard at the window while one searched for (6,3)

I believe the answer is:

looked out

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'kept guard at the window while one' is the definition.
I can't judge whether this defines the answer.

'searched for' is the wordplay.
'searched' becomes 'looked' ('look' can be a synonym of 'search').
'for' becomes 'out' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'looked'+'out'='LOOKED OUT'

Can you help me to learn more?

I've seen this clue in the Evening Standard.

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