Douglas Harper's Etymology Dictionary
yester-
Old English geostran "yesterday," from Proto-Germanic *gester- (cognates: Old High German gestaron, German gestern "yesterday," Old Norse gær "tomorrow, yesterday," Gothic gistradagis "tomorrow"), originally "the other day" (reckoned from "today," either backward or forward), from PIE root *dhgh(y)es- "yesterday" (cognates: Sanskrit hyah, Avestan zyo, Persian di, Greek khthes, Latin heri, Old Irish indhe, Welsh doe "yesterday;" Latin hesternus "of yesterday").
Wiktionary
yester-
pre. 1 (context rare English) Belonging to the day preceding the present; next before the present. 2 Denoting former, earlier, or previous times.