rain day—(Meteorolog y) a day on which the recorded rainfall is not less than 0.01 inch:
- In July the average number of rain days is only four per month.
rainy day—
1. a day having much rain:
- West Mediterranean islands have cooled off and can have rainy days, but walking is still pleasant.
2. (in the phrase “for a rainy day”) for a time of special need in the future:
- We all need money set aside for a rainy day.