Servant giving farewell ahead of time (5)
I believe the answer is:
valet
'servant' is the definition.
(valet is a kind of servant)
'giving farewell ahead of time' is the wordplay.
'giving' means one lot of letters go next to another.
'farewell' becomes 'vale' (I've seen this before).
'ahead of time' becomes 't' (I've seen this in other clues).
'vale' put next to 't' is 'VALET'.
(Other definitions for valet that I've seen before include "Clean (a car); attendant" , "Man's personal attendant" , "Personal serving man" , "Gentleman's gentleman" , "Man's man" .)