Find the word definition

Wiktionary
zeppelin mail

n. mail carried on zeppelins.

Wikipedia
Zeppelin mail

Zeppelin mail was mail carried on zeppelins, the German airships that saw civilian use from 1908 to 1939. Almost every zeppelin flight carried mail, sometimes in large quantities; the covers usually received special postmarks, and a number of nations issued postage stamps specifically intended for use on mail carried by the zeppelins.