Rhumb

from WordNet (r) 3.0 (2006)

rhumb
    n 1: a line on a sphere that cuts all meridians at the same
         angle; the path taken by a ship or plane that maintains a
         constant compass direction [syn: {rhumb line}, {rhumb},
         {loxodrome}]

from The Collaborative International Dictionary of English v.0.48

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]