ˈrəm|līn noun
: a line on the surface of the earth that makes equal oblique angles with all meridians, that is a spiral coiling round the poles but never reaching them, and that is the path of a ship sailing always oblique to the meridian in the direction of one and the same point of the compass
the only projection on which the rhumb line on the earth is reduced to a straight line on the map is the Mercator projection — C.H.Deetz
— called also loxodrome, loxodromic curve