フランス語のm'aiderが英語の俗語化したもので、venez m'aiderから省略されたもの、つまりcome help me、つまりvenezの「来る」、語源的にはcomeと同じ、vue、m'、me、語源的にはmeと同じ、aider、help、語源的にはaidと同じ。後に遭難信号にも使われる。
"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]