Definition of seismic adjective from the Oxford Advanced Learner's Dictionary

     

    seismic

     adjective
    adjective
    BrE BrE//ˈsaɪzmɪk//
     
    ; NAmE NAmE//ˈsaɪzmɪk//
     
    [only before noun]
     
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  1. 1connected with or caused by earthquakes seismic waves
  2. 2having a very great effect; of very great size a seismic shift in the political process
  3. Word Origin mid 19th cent.: from Greek seismos ‘earthquake’ (from seien ‘to shake’) + -ic.
See the Oxford Advanced American Dictionary entry: seismic