It depends what you mean by “vowel” and “word”. There are
two things we mean by the word “vowel” : a speed sound made with the vocal
tract open a letter of the alphabet standing for a spoken vowel (Look up vowel
for a more detailed definition). Cwm and Crwth do not contain the letters a, e,
I, o, u, or y the usual vowels (that is, the usual symbols that stand for vowel
sounds) in English. But in those words the letter ‘w’ simply serves instead,
standing for the same sound that “oo” stands for in the word boom and booth.
Dr., nth (as in “to the nth degree”) and TV also do not contain any vowel
symbols, but they, like cwm and crwth, do contain vowel sounds. Shh, psst, and
mm-hmm do not have vowels, either vowel symbols or vowel sounds. There is Some
controversy whether they are in fact “words”, however. But if a word is “the
smallest unit of grammar that can stand alone as a complete utterance,
separated by spaces in written language and potentially by pauses in speech” as
it is according to The Cambridge Encyclopedia of Language), then those do
qualify. Psst, though, is the only one that appears in the Oxford English
Dictionary.
