Look ahead, stupid fellow! (4)

I believe the answer is:

loon

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'stupid fellow' is the definition.
The definition and answer can be both people as well as being singular nouns.
Perhaps there's a link between them I don't understand?

'look ahead' is the wordplay.
'look' becomes 'lo' (archaic exclamation meaning 'look!').
'ahead' becomes 'on' (synonyms).
'lo'+'on'='LOON'

Can you help me to learn more?

(Other definitions for loon that I've seen before include "Diver; silly person" , "Simple-minded person" , "Noddy" , "Fish-eating diving bird" , "Fool" .)

I've seen this clue in the Evening Standard.

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