Carve with acid (4)
I believe the answer is:
etch
'carve with acid' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for etch that I've seen before include "Cut; engrave" , "Inscribe" , "Cut (design) on surface" , "Wear away by chemical reaction" , "Engrave; fix firmly" .)