期 pairs 其 (sound) with the moon 月 — because before clocks, the moon WAS the calendar. A 期 is a moon-measured stretch of time: a period, a term, an appointed date.
期 schedules life: 星期 (week — 'star period', with 星), 学期 (school term, with 学), 日期 (date). 期待 is to look forward to — to wait for an appointed time. The lunar root still shows: Chinese festivals follow the moon, and 期 quietly reminds you that time in China was counted in moonlight long before Mondays existed.
The moon 月 marking appointed time — a PERIOD, a TERM.
星期几? literally asks 'star-period how-many?' — days of the week are numbered, not named: Monday is 星期一, 'week-one'.