What word (which doesn't contain the letter y) only has one vowel even though it has nine letters?
(In reply to
re(5): a solution by Penny)
"Excellent" is a word composed of nine letters that also is composed of only one unique vowel, the letter 'e.' Given the broad scope of the problem, I think it could be counted as a valid answer, just not one the author intended. I'm pretty sure (and here I agree with just about everyone else and you included) that the author meant only one instance of a vowel and not multiple instances of just one vowel, and--you're right--strengths would be the only word that fulfills this requirement.
On a side note, is there another word like excellent whose composition does contain nine distinct letters and only one unique vowel?
Maybe there is, but I can't find it.