Having a sharp incline (5)
I believe the answer is:
steep
'having a sharp incline' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for steep that I've seen before include "Having a sharp incline" , "Rising sharply" , "Lofty" , "Unreasonably dear - soak" , "Vertiginous; excessive" .)