Back in bureau, a seriously hairy man (4)
I believe the answer is:
esau
'hairy man' is the definition.
(hairy son of Isaac in the Bible)
'back in bureau a seriously' is the wordplay.
'back' is a reversal indicator.
'in' indicates a hidden word.
'uase' is hidden in the letters of 'bureau a seriously'.
'uase' backwards is 'ESAU'.
(Other definitions for esau that I've seen before include "Jacob's brother in the bible" , "Cheated brother" , "Biblical man who sold his birthright for a mess of pottage" , "Would-be fratricide" , "Elder of the twin sons of Isaac and Rebecca" .)