Engrave, as on glass (4)
I believe the answer is:
etch
'engrave as on glass' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for etch that I've seen before include "Mark" , "Cut into a block used for printing" , "Make deep lines" , "Use acid to design on metal or glass" , "Prepare artwork" .)