Bit of a bluff (4)
I believe the answer is:
crag
'bit of a bluff' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for crag that I've seen before include "Steep rocky cliff" , "Steep rock, peak" , "Rugged rock face" , "Steep or rugged cliff face" , "Steep, overhanging rock" .)