Rhenish fan

Etymology
. So called because all or most of the isoglosses collapse in Hesse and fan out to the west.

Proper noun

 * 1)  A set of isoglosses in West Central German showing how the effect of the  gradually decreases towards the north-west (i.e. towards Low Franconian and Low Saxon)

Translations

 * German:, rheinischer Fächer