From Old English 'geostran daeg' — combining a PIE root for 'yesterday' over 5,000 years old with 'day.'
From Old English 'geostran dæg,' a compound meaning 'the other day' or 'the day before.' The first element, 'geostran' (also 'gēostre, giestran'), derives from Proto-Germanic *gestra- ('the other day, yesterday'), from PIE *ǵʰdʰyes or *ǵʰes- ('yesterday'). The second element is 'dæg' ('day'). The PIE root for 'yesterday' is remarkably well-preserved across Indo-European languages, making it one of the oldest recoverable time words. Key