Ingrain deeply (4)
I believe the answer is:
etch
'ingrain deeply' 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 "Engrave (metal/glass)" , "Carve into surface of something" , "Inscribe" , "Make carvings" , "Engrave; fix firmly" .)