/ Dictionary / Index S seismic: Meaning and Definition of Find definitions for: seis•mic Pronunciation: (sīz'mik, sīs'-), [key] — adj. pertaining to, of the nature of, or caused by an earthquake or vibration of the earth, whether due to natural or artificial causes. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: seismic (Thesaurus) seism seismic gap Related Content Daily Word Quiz: neologism Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language