Traitor with relaxed manner heading for lunch (6)

I believe the answer is:

weasel

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'traitor' is the definition.
(weasel can mean a treacherous person)

'with relaxed manner heading for lunch' is the wordplay.
'with' becomes 'w' (abbreviation).
'relaxed manner' becomes 'ease' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'heading for' suggests taking the first letters.
The initial letter of 'lunch' is 'l'.
'w'+'ease'+'l'='WEASEL'

Can you help me to learn more?

(Other definitions for weasel that I've seen before include "Proverbially deceitful mammal" , "E Wales (anag.)" , "Rat" , "Old jingle 'Pop goes the . . . . . .'" , "Seal we turn into a long thin mammal" .)

I've seen this clue in The Independent.

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