Day  n. 1 time between sunrise and sunset. 2 a 24 hours as a unit of time. B corresponding period on other planets (martian day). 3 daylight (clear as day). 4 time during which work is normally done (eight-hour day). 5 a (also pl.) Historical period (in those days). B (prec. By the) present time (issues of the day). 6 prime of a person's life (have had my day; in my day). 7 a future time (will do it one day). 8 date of a specific festival or event etc. (graduation day; christmas day). 9 battle or contest (win the day).  all in a day's work part of the normal routine. At the end of the day when all is said and done. Call it a day end a period of activity. Day after day without respite. Day and night all the time. Day by day gradually. Day in, day out routinely, constantly. Not one's day day when things go badly (for a person). One of these days soon. One of those days day when things go badly. That will be the day colloq. That will never happen. [old english]