Black tie finally spare (5)
I believe the answer is:
ebony
'black' is the definition.
(similar in meaning)
'tie finally spare' is the wordplay.
'finally' indicates one should take the final letters.
'spare' becomes 'bony' (both can mean very thin).
The final letter of 'tie' is 'e'.
'e'+'bony'='EBONY'
(Other definitions for ebony that I've seen before include "Wood - Boyne (anag)" , "Very dark black" , "hard stuff" , "Black hardwood" , "Tree with blackish wood" .)