[1] : 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
see also:
rhomb rhumb line loxodromic curve loxodromic to sail on a rhumb 

[2] : WordNet (r) 2.0

rhumb
     n : 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, loxodrome
see also:
rhumb line loxodrome 

Rhumb >> R Words
Rhumb, definition of term: Rhumb
rhumb_pag1.html

Rhumb Line >> R Words
Rhumb Line, definition of term: Rhumb Line
rhumb+line_pag1.html