The first of May is traditionally called May Day and is related to the Celtic festival of Beltane and the Germanic festival of Walpurgis Night.  The English have been known to break out in fits of Morris Dancing around May Day.  In many countries May Day is celebrated as International Workers Day or Labor Day.

Mayday as a distress call over radio is much newer.  The Mayday callsign was originated in 1923 by Frederick Stanley Mockford (1897–1962).  A senior radio officer at Croydon Airport in London, Mockford was asked to think of a word that would indicate distress and would easily be understood by all pilots and ground staff in an emergency. Since much of the traffic at the time was between Croydon and Le Bourget Airport in Paris, he proposed the word “Mayday” from the French m’aider. “Venez m’aider” means “come help me.”