(sports) The day of a competition, as opposed to practice games. / (by extension, figuratively) The day when something important is scheduled to happen.

British standard spelling of Labor Day.

(science fiction) A day in Earth time; the period it takes planet Earth to revolve once; a period of 24 hours.

A man-day worked by a woman.

(fandom slang) April 26, as a "fan holiday" celebrating the science-fiction horror franchise "Aliens". The date 4/26 is in reference to fictional planet LV-426 where the Xenomorph was first unveiled.

The date of February 12, an annual celebration of the birth of Charles Darwin in 1809.

Any of various annual commemorative days that mark the start of an era of freedom, such as the end of apartheid in South Africa or the withdrawal of British troops from Malta.

To fix the date of an event, especially one's marriage.

(art) The final day before a public exhibition; originally the day when artists could apply a final coat of varnish to their paintings after they had been hung, now the day when artists can make finishing touches, make sure pictures have been hung the right way up etc., and meet their fellow artists.

(historical) Any day on which business could be legally done, excluding Sundays and public holidays.