Euouae
https://en.m.wikipedia.org/wiki/Euouae
Euouae (/juː.ˈuː.iː/; sometimes spelled Evovae)[1] is an abbreviation used as a musical mnemonic in Latin psalters and other liturgical books of the Roman Rite. It stands for the syllables of the Latin words saeculorum Amen, taken from the Gloria Patri, a Christian doxology that concludes with the phrase in saecula saeculorum. Amen. The mnemonic is used to notate the variable melodic endings (differentiae) of psalm tones in Gregorian chant.
In some cases, the letters of Euouae may be further abbreviated to E—E.[2] A few books of English chant (notably Burgess and Palmer's The Plainchant Gradual) make use of oioueae for the equivalent English phrase, "world without end. Amen".
According to Guinness World Records, Euouae is the longest word in the English language consisting only of vowels, and also the English word with the most consecutive vowels.[3] As a mnemonic originating from Latin, it is unclear that it should count as an English word; however, it is found in the unabridged Collins English Dictionary.[4]