[seis.mic] adj [Gk seismos shock, earthquake, fr. seiein to shake; prob. akin to Av thwaesho fear] (1858) 1: of, subject to, or caused by an earthquake; also: of or relating to an earth vibration caused by something else (as an explosion or the impact of a meteorite)
2: of or relating to a vibration on a celestial body (as the moon) comparable to a seismic event on earth
3: having a strong or widespread impact: earthshaking "~ social changes" -- seis.mi.cal.ly adv