Used to refuse an offer politely, with the implication that one may take it up at a later date: they wanted me to come along for the ride but I took a rain check...- Now now I didn't turn you down I just took a rain check.
- She took a rain check on the invitation to lunch with her colleagues and sought Mel out instead.
- I think I'll take a rain check on that one, Winters.
See parent entry: rain check