Some beautiful sounding words in the English language are mellifluous, serendipity, ethereal, luminescence and syzygy. Dr. Robert Beard, in his book "The 100 Most Beautiful Words in English" includes the words bungalow, dalliance, onomatopoeia, propinquity and tintinnabulation. How beautiful a word sounds is subjective, but such terms typically have multiple syllables, roll off the tongue and are fun to say.
Dr. Robert Beard has edited dictionaries, compiled lists of words, composed poetry and written the "Word of the Day" feature at YourDictionary.com since 2004. "The 100 Most Beautiful Words in English" is Dr. Beard's collection of the language's loveliest sounding words with a brief essay on each. The book also includes a piece on what makes a word beautiful so readers can move beyond the list and make their own day-to-day language more attractive. Dr. Beard explains the way in which English relates to other languages in the world and why we have borrowed so many of our most beautiful words from other cultures.
A combination of words can also sound beautiful. The phrase "cellar door" is considered an example of a combination of syllables that is pleasant to the ear, without describing an object of beauty. J.R.R. Tolkien supported this view when he wrote: "Most English-speaking people...will admit that cellar door is 'beautiful', especially if dissociated from its sense..."