What's the longest word you know?

My godson was telling me about a 28 letter English word, though of course I hadn't heard of it! I'm not sure what the longest word I actually use would be. Perhaps "hypothetically"? I'd be keen to hear of any longer common words. "Incomprehensibilities" is probably the longest I can pronounce, but I don't think I've ever used it! And apparently, hippopotomonstrosesquippedaliophobia is a fear of long words...

In Aboriginal languages it's common to get very long words. Here are a few examples.

birrimarnebarddurrungkurlhdanj = they bowed down to him (in Kuninjku) ngarlpurringkulanytjakitjamunu-latju = we-more-than-2-not-including-you were not intending to play (in Ngaanyatjarra) apentey-angenh-rnem-apeny-weny = not like those who don't follow (in Alyawarr)