The reader is invited to ponder the sentence “Unsociable housemaid discourages facetious behaviour”. What is unusual about it? What property do the words have that is shared by relatively few other words?
The answer, of course, is that each word contains the five vowels A, E, I, O and U exactly once. Most people know that facetious and abstemious are the two most common English words containing the five vowels in their natural order; fewer are aware that unoriental is the most common English word containing the five vowels in reverse order.
Language expert and researcher the late Dmitri Borgmann listed additional words with the vowels in natural and reverse order, and also examined the problem of finding the shortest possible word containing all five vowels (sequoia) – a remarkable feat for a precomputer database era. One lasting regret is that the plural of sequoia isn’t sequoiae, which would have made it a uniquely elegant word to have five vowels in a row (the actual plural is a staid sequoias).
If one admits y as a sixth vowel, it is easy to find an English word containing all six vowels in natural order (facetiously), but the reverse problem is much harder.
Perhaps the best solution is given by Alan Wachtel in the November 1968 Word Ways; he suggested Yuloidea (an obsolete name for the superfamily of millipede).
Here are other words in the dictionary whose unusual features are worthy of recording as footnotes to their individual entries:
aegilops the longest word in the English language to have all of its letters in strict alphabetical order;
smithery contains no fewer than seventeen different pronouns: he, her, hers, him, his, I, it, its, me, my, she, their, theirs, them, they, thy, ye;
triennially: every alternate letter forms a completely different word; the odd-numbered letters form tinily, the even-numbered letters form renal;
uncomplimentary; the longest of three English words that contain all five vowels, once only and in reverse alphabetical order (the others being subcontinental and unnoticeably);
zoosporous is one of the longest words to be composed solely of letters of the second half of the alphabet, M to Z.