A measure of heating or cooling, computed as the integral of a function of time that generally varies with temperature.

(Canada) A holiday commemorating the birthdays of Queen Victoria and the reigning monarch of Canada, falling on the last Monday before May 25.

(idiomatic) An excursion, returning home on the same day.

The day on which a President and a Vice-President of the United States takes office, now on January 20 after a Presidential election, before 1936 on March 4.

(computing, idiomatic) (of vulnerability) newly discovered, and therefore still not fixed and possibly exploited by hackers or other criminals

(computing, idiomatic) vulnerability that has been discovered recently, and is yet unpatched or unmitigated; zero-day vulnerability

(US) A day when one is permitted to not attend work in order to go on a vacation or attend to other matters.

One person's working time for a day, or the equivalent, used as a measure of how much work or labor is required or consumed to perform some task.

For a very long or seemingly endless time.

Current; of the present. / (informal) Designating a present-day version of someone or something in history.