* fabula: This is a general term for "story" or "tale," and could be used if the context makes the fictional nature clear.
* narratio: This means "narrative" or "account," again suitable if the context clarifies it's a fictional narrative.
* libellus: This means "little book," and might be appropriate, especially for a shorter novel.
* volumen: This means "scroll" or "volume," referring to the physical form of the book.
None of these perfectly capture the modern English meaning of "novel," as the concept of the novel as a distinct literary genre didn't exist in classical Latin. You'd need to choose the word that best fits the specific context.