lubber's line

or lubber line


noun Navigation.

a vertical line on the forward inner side of the bowl of a fixed compass, used as a reference mark indicating the heading of a vessel.
Also called lubber's mark, lubber's point.

Origin of lubber's line

First recorded in 1855–65

British Dictionary definitions for lubber line

lubber line

noun

a mark on a ship's compass that designates the fore-and-aft axis of the vessel Also called: lubber's line