Rachmaninoff’s Vocalise (1915) is a wordless song, the last of the Fourteen Songs in Opus 34. Originally, the song was dedicated to soprano Antonina Nezhdanova. As the work is without words, it is the singer who chooses the solitary vowel sound to sing.
that which comes nearest to
expressing the inexpressible, is music.
I often think music is a better way of expressing the inexpressible than words, because it lacks them and so speaks more directly to emotion. That Rachmaninov piece is sublime.