These words refer to things that are commonplace or that occur every twenty-four hours or during daylight. Daily and everyday are the most informal of these. Daily refers most specifically to something that occurs once every twenty-four hours: a daily newspaper; a tantrum that was almost a daily occurrence. It may also refer to things that inevitably occur each day, regardless of number. Give us this day our daily bread. It may even suggest things accounted for by the day or things that differ from one day to the next: a daily record of expenditures; restaurants that have daily menus. Everyday, by contrast, refers almost exclusively to anything usual or ordinary, whether or not it can be strictly said to occur once every twenty-four hours: the everyday life of the town. More specifically it refers to things appropriate for ordinary, humble occasions rather than for special events: everyday clothes. It can even suggest that something is plain or drab: everyday routine.

Quotidian and diurnal are much more formal. Quotidian is the more inclusive of the two in referring to aspects both of daily and everyday . It can indicate something that occurs daily: a quotidian fever. Diurnal suggests something that goes through its cycle of changes once every twenty-four hours: the diurnal motion of the stars.