yst

Old English

ȳst f

storm, tempest, whirlwind, hurricane
- late 9th century, translation of Orosius’ History Against the Pagans
  On þǣm dagum wæs Alexander ġeboren on Crēcum swa swa ān miċel ȳst cōme ofer ealne middenġeard.
  In those days Alexander [the Great] was born in Greece, like a great storm coming over all the Earth.
storm surge, stormtide, rough seas, rough water

Declension of ȳst (strong i-stem)