originates from

PWGmc *hwaþar "which (of the two)" (hwaþar > hwæþær > hwæþer) through pwgmc-to-oe

PGmc *hʷaþera- "who of two?" (hʷaþera- > hʷaþara > hʷaþar > hwaþar > hwæþær > hweþer) through pgmc-to-oe