Honorificabilitudinitatibus, in Latin, means "the state of being able to achieve honours," but it's also an English word and is unusual for a number of reasons. First, according to wikipedia it's "the longest word in the English language featuring alternating consonants and vowels."
Second, it's used exactly once by Shakespeare, in Love's Labour's Lost:
O, they have lived long on the alms-basket of words. I marvel thy master hath not eaten thee for a word; for thou art not long by the head as honorificabilitudinitatibus: thou art easier swallowed than a flap-dragon.
But this single use is considered highly significant by those who believe Francis Bacon wrote all of Shakespeare's works, since honorificabilitudinitatibus happens to be an anagram for "hi ludi, F. Baconis nati, tuiti orbi," which in Latin means "these plays, F. Bacon's offspring, are preserved for the world."
Watch the video below if you need help pronouncing it.