2088: week Sep 2, 2020
Time has many subdivisions, but the more natural ones are related to seasons and the cosmos. 'Month' comes from the same root as 'moon' for instance, but there is a similar situation with 'week'. It comes from the Proto-Germanic root *wikǭ meaning 'change', or alternatively 'bend', as in the cycles of the moon; a week is roughly 1 quarter of a full lunar cycle, but the specific 7-day period was only adopted with the spread of Christianity anyway. This makes the word 'week' also related to 'vicar' and the prefix 'vice-', through the sense of 'alternate'.
Watch a video about the significance of 7 (day week) here.