An Asperity

1. The quality of being harsh or severe in the way one speaks or behaves toward people.[1]

Synonyms: acerbity, harshness, severity, sharpness

2. The quality of being difficult or unpleasant to experience.

Synonyms: harshness, rigour, severity

3. The quality of having a rough or uneven surface.

Synonyms: bumpiness, roughness, ruggedness, unevenness

Antonym: smoothness

4. (countable) Something that is harsh and difficult to endure.
5. (countable) An area that protrudes from a surface.

Synonyms: bump, protuberance

6. (countable, geology) A section of a fault line with high friction, such that there is no movement along this part of the fault except during an earthquake. [since 1981]