Definition of seismic adjective from the Oxford Advanced American Dictionary

     

    seismic

     adjective
    adjective
    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
See the Oxford Advanced Learner's Dictionary entry: seismic