Eh? Which country do you mean, different countries have different dates. New Zealand for example has Labour Day which was enacted considerably prior to May Day memorials in other countries.
But for the US, 1891.
An anniversaryanniversary: the annual celebration of an event on that day of a previous year
An event can typically be called annual after it has occurred in two consecutive years. However, to strengthen the claim of being an annual event, many organizations prefer to wait until a third occurrence to ensure consistency and establish a tradition. Therefore, while two occurrences can suffice, a third is often seen as more definitive.
The proper word for the completion of one year is "anniversary." This term is commonly used to mark the annual recurrence of a significant event, such as a wedding or the founding of an organization. It signifies a celebration or remembrance of that event occurring one year ago.
"Annual" refers to something that occurs once a year. It can pertain to events, reports, or activities that are scheduled to happen every twelve months, such as an annual meeting, an annual report, or seasonal festivals. The term emphasizes the regularity and recurrence of the event or item on a yearly basis.
Annual
1891
An annual event occurs once a year.
1789
Annual event
Once a year is called an annual event.
Once a year is called an annual event.
Basketball became an official Olympic event in 1936. It was included for the first time at the Berlin Games. Prior to this, the sport had been played in exhibition matches at the Olympics since 1904, but it was not until 1936 that it was formally recognized as a medal event.
Something that happens once a year.
An event of some sort that happens twice a year.
An anniversaryanniversary: the annual celebration of an event on that day of a previous year
An annual event
The Super Bowl is an annual event because it occurs once a year, at the end of each NFL season.