Picture the scene, if you will. You're in Vienna standing on the banks of the blue Danube¹ taking in the majesty of the river that cuts a swathe across Europe leaving waltzes, romance and boat tours in its wake. There's a long history of shipping on the Danube and sure enough there's some information in your guidebook about it. Alas, it's all in German. Not to worry, you've got your trusty phrase book at hand and so you set about finding out what this Donau­dampfschiffahrts­elektrizitäten­haupt­betriebs­werkbau­unterbeamten­gesellschaft that the guide book mentions is all about.

Pardon?

How do you say that?   Donau­dampfschiffahrts­elektrizitäten­haupt­betriebs­werkbau­unterbeamten­gesellschaft, or if we split the compound noun up into its component parts Donau - dampfschiffahrts - elektrizitäten - haupt - betriebs - werkbau - unterbeamten - gesellschaft, is the longest German word ever published² at 79 letters long. One can argue that after the spelling reform of 1996³ the word should have an extra 'f' in the -schiff(f)ahrts- component bringing the total number of letters up to a nice round 80, but as a proper noun it can retain the double (as opposed to triple) f and anyway, it already has 79 letters and so it really doesn't need another one.

It's also handy to note that Donau­dampfschiffahrts­elektrizitäten­haupt­betriebs­werkbau­unterbeamten­gesellschaft originates in Austria, as Austrian German can differ substantially from German German.

So What Does That Mean Then?

Donau­dampfschiffahrts­elektrizitäten­haupt­betriebs­werkbau­unterbeamten­gesellschaft translates into English as the Association for Subordinate Officials of the Head Office Management of the Danube Steamboat Electrical Services, which was a subdivision of the pre-war Vienesse shipping company known as Donau­dampfschiffahrts­gesellschaft (DDSG)⁴ that transported both cargo and passengers along the Danube.

And People Actually Use This Word?

Much like the word pneumono­ultra­microscopic­silico­volcano­coniosis in English with its paltry 45 letters, Donau­dampfschiffahrts­elektrizitäten­haupt­betriebs­werkbau­unterbeamten­gesellschaft is not used a great deal in everyday conversation; even the most ardent of sesquipedalians would be hard pressed to use it on even a semi-regular basis.

The nature of German grammar is such that compound nouns are a common concept in the language and can be created quite easily. So much so, in fact, that generally when a German linguist sees a newly created word starting with Donau­dampfschiffahrts- they just roll their eyes and resign themselves to the fact that someone has had yet another attempt at creating the longest German word. The whole craze for this seems to have started with the word Donau­dampfschiffahrts­gesellschafts­kapitän which was the correct way to address a captain of any DDSG ship; this word soon became a prefix to such words as Donau­dampfschiffahrts­kapitäns­mütze (meaning the DDSG Captain's hat), Donau­dampfschiffahrts­kapitäns­witwe (his widow) and Donau­dampfschiffahrts­kapitäns­pfeife (the very same Captain's pipe); the variations are endless and more words can be added to create a word of hippopota­monstro­sesquipedalian⁵ proportions.

Incidentally, the longest everyday German word still has an impressive 39 letters: Rechts­schutz­versicherungs­gesellschaften, meaning insurance companies which provide legal protection.