2
general::
Phrase(s): save (something) for a rainy day [and] put something aside for a rainy day; hold something back for a rainy day; keep something for a rainy day
Fig. to reserve something—usually money—for some future need. • I’ve saved a little money for a rainy day. • Keep some extra allowance for a rainy day.
McGrawhill's American Idioms And Phrasal Verbs