Solution to receding hairline uneasy Rupert adopts (5)
I believe the answer is:
'solution to receding hairline' is the definition.
(as in hair syrup)
'uneasy rupert adopts' is the wordplay.
'adopts' indicates the answer is hidden within the clue (the answer has been adopted by the clue).
'SYRUP' is hidden within 'uneasy rupert'.
(Other definitions for syrup that I've seen before include "Viscous liquid" , "Sticky sugar spread" , "Sweet stuff" , "cough mixture?" , "Sugary ingredient" .)