Wood suitable for the mast (5)

I believe the answer is:

beech

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'wood' is the definition.
(beech is a kind of wood)

I don't understand the rest of the clue.

(Other definitions for beech that I've seen before include "Tree (with green or copper leaves)" , "It has branches" , "for mast?" , "Common deciduous tree" , "Nut-bearing tree" .)

I've seen this clue in the Evening Standard.

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