seismic

The English spelling <ei> is particularly opaque.

• Other examples with the pronunciation eɪ include beige, deign, feint, rein, surveillance, vein.
• Others with iː include codeine, protein, seize, Keith, Leith, Neil(l), Reid.
• Others with aɪ include eider, kaleidoscope, Eileen, Brunei and German-derived words or names such as zeitgeist, Einstein. There is also the Greek-derived seismic.

At least, that’s the way I assumed everyone pronounces seismic: ˈsaɪzmɪk. But the other day I heard the politician Chris Huhne hjuːn speak of ‘a ˈseɪzmɪk shift’ in something or other.

Ancient Greek σεισμός seismós ‘a shaking, shock’ had eː during the classical period, yielding i in Modern Greek. The regular development in post-GVS English is aɪ, which we also see in dinosaur ˈdaɪn-, based on δεινός deinós ‘terrible’ (though dinosaur is of course a relatively recent coinage). Within the same discipline of geology and paleontology we also have pleistocene ˈplaɪstə(ʊ)siːn (Greek πλεῖστος pleîstos ‘most’). There is also paradise ˈpærədaɪs, borrowed from Iranian via Greek παράδεισος parádeisos.

As can be seen from these examples, the English spelling is sometimes ei and sometimes simple i. At seismic the OED comments that ‘the normal form would be *sismic’.

English is unusual among languages in that there are a large number of words whose spelling is firmly fixed, but whose pronunciation is not.