Portoise \Por"toise\, n. [Perhaps fr. OF. porteis portative, portable.]

(Naut.) The gunwale of a ship.

To lower the yards a-portoise, to lower them to the gunwale.

To ride a portoise, to ride an anchor with the lower yards and topmasts struck or lowered, as in a gale of wind.

Source: Webster's Revised Unabridged Dictionary (1913)