warrant

The noun comes from Middle English warant, meaning protector or protection, borrowed through Anglo-Norman and Old Northern French warant/warand, variants of Old French guarant (assurance, guarantee, protector), which trace back to Frankish *warand, the present participle of *warjan, "to fend off, to stop, thwart." The verb form followed the same route, from Middle English waranten, meaning to protect, assure, or promise.

It began as a word for a guard or shield against harm, then shifted toward the idea of a guarantee or promise, and eventually settled into the sense of official authorization we use today.

It's cognate with Old High German werento, meaning guarantor, showing the same root sense of someone who vouches for or protects another.