Sometime colleagues of Y

• Elementary quintet
• Y's associates?
• The five vowels
• Key parts of a so-called supervocalic word
• Useful parts of the alphabet
• Facetious, half-serious, abstemious quintet?
• Necessary letters
• Elements found once each in 1-, 15-, 57-, 62-Across, and 30-Down
• Basic quintet

Wikipedia Word definitions in Wikipedia
' AEIOU ' is a 1979 Czechoslovak film. The film starred Josef Kemr .