sea gate

a navigable channel giving access to the sea.

Origin of sea gate

First recorded in 1860–65

When two ships are thrown on board one another by a wave, they are said to be in a sea-gate.

The Sailor's Word-Book |William Henry Smyth
It was outside the sea-gate, however, that the siege was pressed most hardly.

The Harlequin Opal, Vol. 3 (of 3) |Fergus Hume
Let the muckrakers worry and plan all they please for a sea-gate and a nation that's to run with its brains removed.

The Harbor |Ernest Poole
The fort was built in the form of a pentagon, with a sort of sea-gate opening on the bay, for the easy launching of the pinnaces.

On the Spanish Main |John Masefield

A long rolling swell: when two ships are thrown aboard one another by its means, they are said to be in a sea-gate.

The Sailor's Word-Book |William Henry Smyth