high sea

From Middle English hey see, hey se, from Old English hēahsǣ (“the high sea, the deep”), equivalent to high +‎ sea.

high sea (plural high seas)

1. The sea when it is very rough due to strong winds and storms, such that the sea encroaches much further inland than is normal, often causing damage.

   The ship eventually broke in half in high sea and winds.

high sea (uncountable)

1. Alternative form of high seas (“open ocean”)