Euouae or Evovae is an abbreviation used in Latin psalters and other liturgical books to show the distribution of syllables in the differentia or variable melodic endings of the standard Psalm tones of Gregorian chant. It derives from the vowels in the words "saeculorum Amen" of the lesser doxology or Gloria Patri, which ends with the phrase In saecula saeculorum, Amen. In some cases the letters EUOUAE can be further shortened to E----E. A few books of English chant (notably Burgess & Palmer's The Plainchant Gradual, Wantage 1962) make use of 'oioueae' for the equivalent phrase "World without end. Amen."
According to the Guinness Book of World Records, at six letters long, "Euouae" is the longest word in the English language made up of nothing but vowels, and also the English word with the most consecutive vowels. As a mnemonic coming from Latin, it is unclear that it should count as an English word; however, it is found in the unabridged Collins English Dictionary.
A similar abbreviation, Aevia (or Aeuia), was used for Alleluia in medieval Office books. In Venetian and other Italian Office-Books of the 16th century, an equivalent abbreviation Hal'a, or Hal'ah, can be substituted for Aevia.
- Apel, Willi: Gregorian Chant. Bloomington: Indiana University Press, 1990. ISBN 0-253-20601-4.
- Dyer, Joseph: «Roman Catholic Church Music» en Grove Music Online ed. L. Macy.
- Hiley, David: «Chant» in Performance Practice: Music before 1600, eds. Howard Mayer Brown & Stanley Sadie. New York: W. W. Norton, 1990, pp. 37–54. ISBN 0-393-02807-0
- Hiley, David: Western Plainchant: A Handbook. Oxford: Clarendon Press, 1995. ISBN 0-19-816572-2.
- Levy, Kenneth: «Plainchant» in Grove Music Online ed. L. Macy.
- Berry, Mary. "Evovae [Euouae]" in Grove Music Online ed. L. Macy.[full citation needed]
- "Longest English Word Consisting Only of Vowels". Guinness World Records. Retrieved 2016-01-23.
- "euouae". Collins English Dictionary. Retrieved 2016-01-23.
- William Smyth Rockstro (1900). "Aevia". In Grove, George. A Dictionary of Music and Musicians. London: Macmillan and Company.