'To sail on a rhumb' definitions:

Definition of 'To sail on a rhumb'

From: GCIDE

Rhumb \Rhumb\, n. [F. rumb, Sp. rumbo, or Pg. rumbo, rumo, probably fr. Gr. ??? a magic wheel, a whirling motion, hence applied to a point of the compass. See Rhomb.] (Navigation) A line which crosses successive meridians at a constant angle; -- called also rhumb line, and loxodromic curve. See Loxodromic. [1913 Webster]
To sail on a rhumb, to sail continuously on one course, following a rhumb line. [1913 Webster]