If you watch cop shows, you know that a warrant is something police need to get into your house — a permission slip from a judge.
It's a noun! It's a verb! It's a word that warrants our attention! As a noun, it's the piece of paper they show you through the keyhole during an investigation. It's also a reason for doing something, or a promise (think of the warranty on your new car, the promise that it'll work for a certain amount of time). As a verb, it means to make something seem reasonable or necessary, such when the ticking suitcase warrants bringing in the bomb squad, or when the teenager's sneaking in late again warrants a stricter curfew.