franked; franking; franks transitive verb 1 a : to mark (a piece of mail) with an official signature or sign indicating the right of the sender to free mailing b : to mail free c : to affix to (mail) a stamp or a marking indicating the payment of postage 2 : to enable to pass or go freely or easily frankable ˈfraŋ-kə-bəl adjective franker noun

https://www.merriam-webster.com/dictionary/frank