Commons' leader leaving in wooden box (6)

I believe the answer is:

coffin

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

'wooden box' is the definition.
'coffin' can be an answer for 'box' (coffin is a kind of box). I'm not sure about the 'wooden' bit.

'commons' leader leaving in' is the wordplay.
'leader' says to take the initial letters.
'leaving' becomes 'off' (as in 'I'm off').
The initial letter of 'commons' is 'c'.
'c'+'off'+'in'='COFFIN'

Can you help me to learn more?

(Other definitions for coffin that I've seen before include "Corpse's chest" , "Casket for the dead" , "Box for a corpse" , "Box for the dead" , "Sarcophagus" .)

I've seen this clue in The Guardian.

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