save, keep, etc. something for a rainy dayidiomPart ofdaysave, keep, etc. something for a rainy daysave, keep, etc. something for a rainy day — idiomidiom1. To save something, especially money, for a future time of need.1.idiomDefinitionTo save something, especially money, for a future time of need.ExampleI put some money aside for a rainy day.She saved the extra cookies for a rainy day.