I suspect that many readers will have noticed that all the vowels (including Y) occur at odd positions in the alphabet (let's call them odd letters). This led me to think of the set of words using only odd letters.
"Wacky Words and Steiner Systems,"
Word Ways: Vol. 45
, Article 6.
Available at: http://digitalcommons.butler.edu/wordways/vol45/iss4/6