Same word as warrant:

accreditation, assurance, authentication, authority, basis, carte blanche, certificate, commission, credential, credentials, ducat, earnest, foundation, go-ahead, green light, guarantee, license, official document, okay, pass, passport, pawn, permission, permit, pledge, right, sanction, security, shingle, sticker, subpoena, summons, tag, testimonial, ticket, token, verification, warranty, word