May Day

noun
1.
the first day of May, long celebrated with various festivities, as the crowning of the May queen, dancing around the Maypole, and, in recent years, often marked by labor parades and political demonstrations.
Origin
1225-75; Middle English

Mayday

[mey-dey] /ˈmeɪˌdeɪ/
noun
1.
the international radiotelephone distress signal, used by ships and aircraft.
Origin
1925-30; < French (venez) m'aider (come) help me!
British Dictionary definitions for May Day

May Day

noun
1.
  1. the first day of May, traditionally a celebration of the coming of spring: in some countries now observed as a holiday in honour of workers
  2. (as modifier): May-Day celebrations

Mayday

/ˈmeɪˌdeɪ/
noun
1.
the international radiotelephone distress signal
Word Origin
C20: phonetic spelling of French m'aidez help me
Word Origin and History for May Day

"first of May," mid-15c. Accounts of merrymaking on this date are attested from mid-13c. Synonymous with "communist procession" from at least 1906. The May Queen seems to be a Victorian re-invented tradition.

mayday

"distress call," 1923, apparently an Englished spelling of French m'aider, shortening of venez m'aider "come help me!" But possibly a random coinage with coincidental resemblance:

"May Day" Is Airplane SOS
ENGLISH aviators who use radio telephone transmitting sets on their planes, instead of telegraph sets, have been puzzling over the problem of choosing a distress call for transmission by voice. The letters SOS wouldn't do, and just plain "help!" was not liked, and so "May Day" was chosen. This was thought particularly fitting since it sounds very much like the French m'aidez, which means "help me." ["The Wireless Age," June 1923]