Style served up in Waldorf Astoria (4)
I believe the answer is:
afro
'style' is the definition.
(Afro is a type of hairstyle)
'up in waldorf astoria' is the wordplay.
'up' says the letters should be written backwards (in down clue: letters go upwards).
'in' indicates a hidden word.
'orfa' can be found hidden inside 'waldorf astoria'.
'orfa' written backwards gives 'AFRO'.
'served' is the link.
(Other definitions for afro that I've seen before include "Shock description" , "Style of haircut" , "One cut" , "Styling done to hair" , "Type of hairstyle - from Africa" .)