The wood where once one walked! (5)
I believe the answer is:
plank
'the wood' is the definition.
(thesaurus)
'once one walked' is the wordplay.
I cannot really see how this works, but
'one' could be 'an' (an apple is one apple) and 'an' is found in the answer.
This explanation may well be incorrect...
'where' is the link.
Can you help me to learn more?
(Other definitions for plank that I've seen before include "Building timber" , "item in political party's programme" , "Long piece of wood" , "Length of sawn timber" , "Proverbially thick piece of wood" .)