(astronomy) The rotational period of Earth; the time in which Earth rotates exactly 360 degrees around its axis, measured relative to the stars (about 23 hours, 56 minutes, 4 seconds).

(astronomy) One day of sidereal time; the time in which Earth rotates once around its axis, relative to the point of the vernal equinox (about 23 hours, 56 minutes, 4 seconds).

(UK) Alternative form of day laborer

As frequently as every day; daily.

(astronomy, physics) A unit of length equal to the distance light travels in one day

Daybreak.

(idiomatic) To seriously regret one's actions.

(idiomatic) One who gets up early in the morning or goes to bed early.

plural of day trader

(computing) Alternative spelling of zero-day.