A compressional wave of air had been started in the far north and had spread out over the earth with the velocity of sound.
The first indication of an earthquake is often a sharp thud, signaling the arrival of compressional waves.
c.1400, from Middle French compression (14c.), from Latin compressionem (nominative compressio) "a pressing together," noun of action from past participle stem of comprimere (see compress (v.)). Related: Compressional. Compressional wave is attested from 1887.
compression com·pres·sion (kəm-prěsh'ən)
The state of being compressed.
See data compression.