Make a notch (6)
I believe the answer is:
indent
'make a notch' is the definition.
(indenting is a kind of making a notch)
This is the entire clue.
(Other definitions for indent that I've seen before include "Deep recess or notch" , "Make recesses or notches in" , "Deep recess; official requisition" , "Set in from the margin" , "Official order" .)