Steep drop-off (5)
I believe the answer is:
cliff
'steep drop-off' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for cliff that I've seen before include "A sheer rock face, in mountain or by sea" , "stony face?" , "Sir - - Richard" , "Steep high rockface" , "-- Richard, singer" .)