Mark a pig going over some wood (8)
I believe the answer is:
mahogany
'wood' is the definition.
(I know that mahogany is a type of wood)
'mark a pig going over some' is the wordplay.
'mark' becomes 'm'.
'pig' becomes 'hog' (synonyms).
'going over' means one lot of letters go next to another.
'some' becomes 'any' (similar in meaning).
'm'+'a'+'hog'+'any'='MAHOGANY'
(Other definitions for mahogany that I've seen before include "Hogmanay? (anag)" , "Tropical timber" , "Wooden" , "Old Cornish drink" , "tree" .)