franking vs postage franking

As nouns, postage franking is a hyponym of franking; that is, postage franking is a word with a more specific, narrower meaning than franking:

• franking: device or marking such as postage stamp, printed or stamped impressions, codings, labels, manuscript writings, or any other authorized form of markings affixed or applied to mails to qualify them to be postally serviced.
• postage franking: postage stamps, or any other markings recognized and accepted by the postal system or systems providing service, which indicate the payment of sufficient fees for the class of service which the item of mail is to be or had been afforded.