Here's a 19-syllable (enneakaidecasyllabic) word that contains each vowel at least twice: pneumonoultramicroscopicsilicovolcanoconioses It's the plural of: pneumonoultramicroscopicsilicovolcanoconiosis which only contains a single e. It's listed in Merriam-Webster: https://www.merriam-webster.com/medical/pneumonoultramicroscopicsilicovolcan... Tom Bill Gosper writes:
Everybody knows FACETIOUS and ABSTEMIOUS. (Which also have the vowels in order, and have adverbs if you demand y.) But can you find a disyllabic less QUESTIONABLE than HOUSEPAINT?
I was shocked when Select[WordData[], ContainsAll[Characters@#, Characters@"aeiou"] &] returned 6899 hits. But most were multiword phrases like AMMONIUM NITRATE and VIRTUAL MEMORY. Precluding " " still left 1093(!), including some cheats like ACRYLONITRILE-BUTADIENE-STYRENE ("The three major food groups!" —Beldar Conehead)
There is at least one aeiou single word nation, chemical element, common vegetable, hideous parasite, medical condition, impossibly common word (automobile, inoculate) . . . I wonder if it's a quiz show category. —rwg