One in front resembling a peacock (4)

I believe the answer is:

vain

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'resembling a peacock' is the definition.
I can't tell whether this definition defines the answer.

'one in front' is the wordplay.
'one' becomes 'i' (Roman numeral).
'in' is an insertion indicator.
'front' becomes 'van' (I've seen this in another clue).
'i' inserted into 'van' is 'VAIN'.

Can you help me to learn more?

(Other definitions for vain that I've seen before include "Worthless" , "Pointless; narcissistic" , "Concieted or pointless" , "Conceited or unavailing" , "thoughtless" .)

I've seen this clue in The Times.

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