What term refers to the author's choice of words and the level of vocabulary used in a story?

The term that refers specifically to the author's choice of words and the level of vocabulary used in a story is diction. Diction encompasses not just the words themselves but also the connotations and nuances they carry, which can greatly affect the tone and meaning of the text. An author’s diction can reflect their character's background, emotions, and even the setting of the story, contributing to the overall impact of the narrative on the reader.

In contrast, syntax pertains to the arrangement of words and phrases to create well-formed sentences, while tone refers to the emotional quality or attitude of the writing. Style, on the other hand, encompasses broader elements including diction, syntax, and tone, representing the author's unique voice or manner of expression in their writing. Therefore, diction is the most precise term in this context when discussing word choice and vocabulary specifically.