An Etymological Dictionary of Astronomy and Astrophysics

1. Roughness or unevenness of surface.
   

2. Physics: A microscopic projection on a metal surface resulting from normal surface finishing processes.
   

3. Geology: A site on a → fault surface where the two sides are held together by an area of higher strength than the areas surrounding it. When the stress on the fault exceeds the strength of the asperity, the asperity fails as an → earthquake.

Etymology (EN): M.E. asperite, from O.Fr. asperité “difficulty, painful situation,” from L. asperitas,
from asper “rough, harsh,” of unknown origin.

Etymology (PE): From zaft “thick, gross, rude,” (Steingass, Dehxodâ), + noun suffix -i.