A number on a piece of wood (5)

I believe the answer is:

tenon

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'a piece of wood' is the definition.
I can't tell whether this defines the answer.

'a number on' is the wordplay.
'a number' becomes 'ten' (ten is a number).
'ten'+'on'='TENON'

Can you help me to learn more?

(Other definitions for tenon that I've seen before include "Join" , "Wooden projection shaped to fit in a mortise joint" , "Projection used in a mortise joint" , "Saw; joint" , "Tongue of wood, fits into mortise" .)

I've seen this clue in The Irish Independent.

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