Formal:
* Inclined plane: A technical term for any sloping surface.
* Gradient: Used in surveying and engineering to describe the steepness of a slope.
Informal:
* Hill: A general term, but it can be used to emphasize its steepness.
* Steep incline: Emphasizes the verticality of the slope.
* Mountain: Used for very steep, high hills.
* Cliff: If the hill is so steep it resembles a vertical drop.
* Escarpment: A steep slope, often formed by erosion.
* Slope: A general term, but can be used to emphasize the incline.
* Grade: Used in transportation to describe the steepness of a road.
Idioms:
* Heartbreaker: Used for a particularly difficult hill to climb.
* Beast: Used for a very challenging hill.
The best term to use depends on the specific situation and the desired level of formality.
