Urge sorceress to hide face (4)
I believe the answer is:
itch
'urge' is the definition.
(I know that urge can be written as itch)
'sorceress to hide face' is the wordplay.
'sorceress' becomes 'witch' (synonyms).
'to hide face' means to remove the first letter (I've seen 'hiding face' mean this (the first letter is the word's 'face')).
'witch' with its initial letter taken away is 'ITCH'.
(Other definitions for itch that I've seen before include "Niggling skin sensation" , "Contagious skin infection" , "Skin sensation; desire" , "It must be scratched" , "Irritate" .)