The plural of day is days.

day[de?]

n. Day; day; era. The basic meaning of day is "one day", which refers to a period of twenty-four hours and is a countable noun. It can also refer to "daytime, daytime", and can be used as both a countable and uncountable noun, usually without an article. Day can also mean "working day", which refers to the working time within 24 hours a day. It is a countable noun. Day can also be used as "period; era; lifespan". It is often used in the plural form. If it is used in the singular, it must be used with possessive pronouns such as my and their. Day also means "heyday, golden age". It is a singular noun and is not used in the plural form. Day sometimes means "victory, competition, battle". It is an uncountable noun preceded by the definite article. Day is often used in phrases expressing legal or religious holidays without an article before it. day can be used as a quantifier, and a day can mean "every day". When the word modified by the attributive clause is day, the relative words that/when/which are often omitted. For example: His father died the day when he was born. His father died on the day he was born. Some dictionaries believe that day and night and night and day have somewhat different meanings: day and night equals continuously, which is used when day is the main focus, and night and day is equal to always, which is used when night is the main focus. In fact, , both are now used without distinction, both meaning "day and night, day and night". The day before yesterday (the day before yesterday), the day after tomorrow (the day after tomorrow) and other phrases can be omitted in American English. For example: He left for London (the) day before yesterday. He left for London (the) day before yesterday.