seis ‧ mic /ˈsaɪzmɪk/ BrE AmE adjective [only before noun]
[ Date: 1800-1900 ; Language: Greek ; Origin: seismos 'shock, earthquake' , from seiein 'to shake' ]
1 . technical relating to or caused by ↑ earthquake s :
increased seismic activity
2 . very great, serious, or important:
seismic changes in international relations