A plank where it may be walked? (6)

I believe the answer is:

aboard

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

'a plank where it may be walked?' is the definition.
I can't tell whether this defines the answer.

'a plank' is the wordplay.
'plank' becomes 'board' (synonyms).
'a'+'board'='ABOARD'

Can you help me to learn more?

(Other definitions for aboard that I've seen before include "On an aircraft" , "... [CRUISE SHIP] here, perhaps" , "A poet penning nothing on vessel" , "on base" , "on gig, perhaps?" .)

I've seen this clue in The Sun.

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