German orthography
Compound words, including nouns, are written together, e.g. "Haustür" (Haus+Tür; house door), "Tischlampe" (Tisch+Lampe; table lamp), "Kaltwasserhahn" (Kalt+Wasser+Hahn; cold water tap/faucet). This can lead to long words: the longest word in regular use, "Rechtsschutzversicherungsgesellschaften" ("legal protection insurance companies"), consists of 39 letters; while the longest German word ever published ("Donaudampfschiffahrtselektrizitätenhauptbetriebswerkbauunterbeamtengesellschaft", "Association for subordinate officials of the head office management of the Danube steamboat electrical services") has 79 letters.
Euouae
According to the "Guinness Book of World Records", at six letters long, "Euouae" is the longest word in the English language made up of nothing but vowels (the v spelling notwithstanding), and also the English word with the most consecutive vowels. As a mnemonic coming from Latin, it is unclear that it should count as an English word; however, it is found in the unabridged Collins English Dictionary.