Beast with face of dark hair (5)
I believe the answer is:
beard
'hair' is the definition.
(beard is a kind of hair)
'beast with face of dark' is the wordplay.
'beast' becomes 'bear' (bear is a kind of beast**).
'with' says to put letters next to each other.
'face of' suggests taking the first letters.
The initial letter of 'dark' is 'd'.
'bear'+'d'='BEARD'
(Other definitions for beard that I've seen before include "hair extension" , "In good health; very" , "SECOND PART OF 14" , "Whiskers" , "Vandyke, perhaps" .)