take a rain check said when politely refusing an offer, with the implication that you may take it up at a later date. North American

☞ A rain check is a ticket given to spectators at US sporting events enabling them to claim a refund of their entrance money or gain admission on another occasion if the event is cancelled because of rain. The rain-check system is mentioned as operating in US sports grounds in the late 19th century; the figurative use of the word dates from the early 20th century.