- Having to do with elastic waves. Energy may be transmitted through the body of an elastic solid by body waves of two kinds: P-waves (compressional waves) or S-waves (shear waves) (see P-waves, S-waves), or along boundaries between media of different elastic properties by head waves and surface waves (q.v.). Equated with "elastic," often with "acoustic" and "sonic."
- Having to do with natural earthquakes. Derived from the Greek "seismos" meaning "shock." While seismic is an adjective, it is frequently used as a noun.