warranty

Most cars and toys come with a warranty, a written guarantee that the product will not fail within a certain amount of time. If it does, the manufacturer will repair or replace it for free.

Many people talk about the way appliances break the day after their warranty expires. The word itself is a Middle English variant on the word, guarantee. Both words mean similar things, but warranty is more specific. I can guarantee you that I will pick you up by seven so we can get to the game on time, but I would not issue a warranty about it.