Rhūmb, n.

noun

(rŭm, 62) (Synop., § 130), n. [Fr. rumb, Sp. rumbo, Pg. rumbo, rumo, It. rombo. See RHOMB.] (Navigation.) Any given point of the compass; a line making a given angle with the meridian; a rhumb-line.

To sail on a rhumb, to sail continuously on one course.