The reference here is to the "may-day" celebrations formerly widely observed in Europe, but now nearly disappeared.
On a may-day of sunshine like the present, the Taro is a gentle stream.
Upon the Common, there still lingered a breath of the may-day festivitiy.
The change of purpose supported his belief that a may-day jest was forward.
may-day has always been celebrated in England with rustic dances and festivities.
Well then, sir, are you going to the may-day party at Shadynook?
Surely of all the lovers that went to keep a may-day tryst, none ever went more sweet and gay than Jenny.
They skipped not in answer to the adagio movement in the may-day Symphony.
The flowers of may-day foretold the harvest, its rosy apples and its yellow ears of corn.
The children are invited to the parks for may-day and romping-day festivals.
"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.
"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]