σάλος, -ου, ὁ [in LXX for מוֹט, etc. ;] in poets and late prose, a tossing, as of an earthquake; esp. the tossing, the rolling swell of the sea: Luk.21:25.† (AS)
Thayer:
1) the tossing or swell of the sea
σάλος
salos
sal'-os
Probably from the base of G4525; a vibration, that is, (specifically) billow