A vocable is a non-lexical utterance; word-like sounds with meaning. For example: The vocable of assent... uh-huh The vocable of denial... uh-uh The vocable of error... uh-oh Or saying 'I don't know' without opening your mouth by humming a low note, then a high note, then a low note again. What other vocables do you use in your writing?
The vocable of a Sicilian brass band concluding a song: bada bing bada boom! The vocable of an English one not concluding one: tum te tum... The vocable of an Anglian typing into a webform: da-də-da-də-dah... I suspect lots of these can't be written down satisfactorily. They might linger outside the written corpus for centuries while they overthrow the semiotic foundations of an entire vowel family.