Quiz: Remember the definition of mal de mer?
Old English hwæðer, hweðer "which of two, whether," from Proto-Germanic *khwatharaz (cf. Old Saxon hwedar, Old Norse hvarr, Gothic huaþar, Old High German hwedar "which of the two," German weder "neither"), from interrogative base *khwa- "who" (see who) + comparative suffix *-theraz (cf. Sanskrit katarah, Avestan katara-, Greek poteros, Latin uter "which of the two, either of two," Lithuanian katras "which of the two," Old Church Slavonic koteru "which"). Its comparative form is either. Phrase whether or not (also whether or no) recorded from 1650s.