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.
Annual
Yes
one. annual means once a year.
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.
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.
Once a year. An annual event only happens once a year, and happens every year.