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n. [ Gr. 'y^ psilo`n bare, mere, simple y. ] The 20th letter (Υ, υ) of the Greek alphabet, a vowel having originally the sound of &oomacr_; as in room, becoming before the 4th century b. c. that French u or Ger. ü. Its equivalent in English is u or y. [ Webster 1913 Suppl. ]