Wood, European, thin (5)
I believe the answer is:
ebony
'wood' is the definition.
(ebony is a kind of wood)
'european thin' is the wordplay.
'european' becomes 'e' (abbreviation e.g. EU).
'thin' becomes 'bony' ('bony' can be similar in meaning to 'thin').
'e'+'bony'='EBONY'
(Other definitions for ebony that I've seen before include "Hard block tropical wood" , "Tree with blackish wood" , "Tree having black wood" , "Black hardwood" , "Wood - Boyne (anag)" .)