Is it ensure, insure, or assure?
mid-15c., from Middle French euphonie, from Late Latin euphonia, from Greek euphonia "sweetness of voice," from euphonos "well-sounding," from eu- "good" (see eu-) + phone "sound, voice," related to phanai "speak" (see fame (n.)).
Hence, euphonium (1865), the musical instrument. Related: Euphonic; euphonious.
sound patterns used in verse to achieve opposite effects: euphony is pleasing and harmonious; cacophony is harsh and discordant. Euphony is achieved through the use of vowel sounds in words of generally serene imagery. Vowel sounds, which are more easily pronounced than consonants, are more euphonious; the longer vowels are the most melodious. Liquid and nasal consonants and the semivowel sounds (l, m, n, r, y, w) are also considered to be euphonious. An example may be seen in "The Lotos-Eaters" by Alfred, Lord Tennyson: "The mild-eyed melancholy Lotos-eaters came." Cacophony, the opposite of euphony, is usually produced by combinations of words that require a staccato, explosive delivery. Inadvertent cacophony is a mark of a defective style. Used skillfully for a specific effect, however, it vitalizes the content of the imagery. A line in Samuel Taylor Coleridge's "Rime of the Ancient Mariner" illustrates cacophony: With throats unslaked, with black lips baked,Agape they heard me call