ember: [OE] Ember goes back to a prehistoric Germanic *aimuzjōn, although it is possible that the modern English word represents a borrowing from the related Old Norse eimyrja rather than a direct line of descent from Old English ǣmyrge. The ember of Ember days [10], incidentally, ‘days following certain Christian festivals’, is a completely different word. It comes from Old English ymbryne ‘circuit’, literally ‘running round’, a compound formed from ymb ‘round’ and ryne ‘course, running’, a relative of modern English run. It was applied to these particular days of the Christian calendar because they ‘come round’ four times a year.
