An Etymological Dictionary of the German Language/Geschwister

by Friedrich Kluge

Geschwister, plur. (prop. neut. sing.), from the equiv. MidHG. geswister (geswisterde), neut. plur., ‘brothers and sisters,’ OHG. giswistar, plur.; akin to Schwester.

Geschwister, read OHG. giswëster.