Why is the ninth month called September?
Old English bidan "to stay, continue, live, remain," also "to trust, rely" (cognate with Old Norse biða, Old Saxon bidan, Old Frisian bidia, Middle Dutch biden, Old High German bitan, Gothic beidan "to wait"), apparently from PIE *bheidh-, an extended stem of one root of Old English biddan (see bid (v.)), the original sense of which was "to command," and "to trust" (cf. Greek peithein "to persuade," pistis "faith;" Latin fidere "to trust," foedus "compact, treaty," Old Church Slavonic beda "need"). Perhaps the sense evolved in prehistoric times through "endure," and "endure a wait," to "to wait." Preserved in Scotland and northern England, replaced elsewhere by abide in all senses except to bide one's time. Related: Bided; biding.