This article is from the alt.usage.english FAQ, by Mark Israel firstname.lastname@example.org with numerous contributions by others.
When I was 6 years old, my schoolmistress said, "There are no
words in the English language that have no vowels. To anyone who
can tell me a word with no vowels, I'll give threepence."
I raised my hand and said, "Shhh."
The mistress looked at me very contemptuously and said, "He
thinks 'shhh' is a word. But it isn't; it's just a sound that
A couple of weeks later, the mistress asked the class, "Has
anyone thought of a word without any vowels yet?"
Another little boy raised his hand and said, "My. Try.
"No," replied the mistress, "'y' is a vowel there. But I'll give
you threepence anyway, because you've been thinking."
After all these years, I *still* think my example was better than
that other little boy's.
I WANT MY THREEPENCE!
The word "vowel" has more than one meaning. From MWCD10:
# 1: one of a class of speech sounds in the articulation of which
# the oral part of the breath channel is not blocked and is not
# constricted enough to cause audible friction; broadly : the one
# most prominent sound in a syllable 2: a letter or other symbol
# representing a vowel -- usu. used in English of a, e, i, o, u, and
# sometimes y
Children are usually taught sense 2, because meaning 1 would be
harder for them to grasp. But since sense 2 is not that *useful*
except as a rough approximation to sense 1 (and on the U.S. TV
show "Wheel of Fortune"), "words without vowels" in sense 2 (such as
"cwm", "nth", "Mrs.", and "TV") are not terribly interesting. Words
without vowels in sense 1 (such as "shhh", "psst", and "mm-hmm")
*are* interesting, because they tell us something about the
phonology of the language.