English A cross sea at Île de Ré. Etymology The swells of the waves, when they meet at right angles, form cross shapes. Noun cross sea (plural cross seas) (nautical) A (dangerous) sea with two wave systems traveling at oblique angles, due to the wind over it shifting direction or the waves of two storm systems meeting. Translations sea Finnish: ristiaallokko German: Kreuzsee (de) f Anagrams acrosses, carosses, sarcosesWikiwand - on Seamless Wikipedia browsing. On steroids.