From Longman Dictionary of Contemporary Englishmaydaymay‧day /ˈmeɪdeɪ/ noun [singular] TCTa radio signal used to ask for help when a ship or plane is in serious danger → SOS
Examples from the Corpus
mayday• Send out a mayday, jump in and wait.• The pilot sent out a mayday.• We sent out a mayday, but your guess is as good as mine if anyone heard it.Origin mayday (1900-2000) French m'aider “help me” 