Hi, have a look at this free online talking dictionary of English pronunciation Just mouse over the pink words to hear them spoken ... www.howjsay.com/index.php?word.

Honorificabilitudinitatibus. (Longest word in Shakespeare's works) Antidisestablishmentarianism. Floccinaucinihilipilification. Pseudopseudohypoparathyroidism. Pneumonoultramicroscopicsilicovolcanoconiosis. The longest place name in the United States (45 letters) is Chargoggagoggmanchauggagoggchaubunagungamaugg. The longest officially recognized place name in an English-speaking country is Taumatawhakatangihangakoauauotamateapokaiwhenuakitanatahu (85 letters) which is a hill in New Zealand.

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I didn't find an English word that is very difficult to pronounce.