A promise that an unaccepted offer will be renewed in the future.
This term comes from baseball, where in the 1880s it became the practice to offer paying spectators a rain check entitling them to future admission for a game that was postponed or ended early owing to bad weather. By the early 1900s the term was transferred to tickets for other kinds of entertainment, and later to a coupon entitling a customer to buy, at a later date and at the same price, a sale item temporarily out of stock.
I can't come to dinner Tuesday but hope you'll give me a rain check.
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