Definition from Wiktionary, the free dictionary
From Kölsch halve Hahn ("half a cock/rooster"). The origin is possibly an order like Kann ich ne Halve hann? ("Can I get half [a sandwich]?"), the last two words of which were then re-interpreted (either by foreigners or jokingly) as halve Hahn.
- The expression is rare in actual usage. Even in thick Ripuarian dialect one generally uses the plain and simple word Kiesbrütche ("cheese sandwich"). However, Halve Hahn is occasionally used as a shibboleth among Rhineland people and can be found on the menus of traditional Colognian pubs (as a humorous knowledge test for foreigners).
- The term is either uninflected, e.g. (accusative) den Halve Hahn, or the first part behaves like a normal German adjective, thus den Halven Hahn, and so on.