(mathematics) equivalence class

a lucky day, auspicious day

(rare) one's birthday

Saturday

the first day of the month (solar or lunar calendar)

(literary) one day, 24 hours / (literary) the daytime, the period from dawn until dusk / (literary) (figuratively) a short period of time

(obsolete) one day, 24 hours / (obsolete) the daytime, the period from dawn until dusk

(rare, obsolete) (all senses appear to be identical as for hitohi above)

(rare) a birthday

a red sun, a bright sun, or the summer sun / a day in the traditional Japanese six-day week which is unlucky except for at noon