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

(skiing) A day of skiing purchased in a ski area, used to measure the number of skiers in any one particular ski area. A season pass is generally considered to be twenty (20) skier days.

plural of leap day

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

plural of degree day

plural of man-day

(Roman Catholic Church) The Tuesday before Easter.

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

(military) Abbreviation of mobilization day.

Work done where the worker is hired and paid one day at a time, with no promise that more work will be available in the future.