Well, verisimilitudinous fiction can also be considered a synonym. It basically means having the appearance of truth or realism, which is a key aspect of realistic fiction. Another one could be 'naturalistic fiction'. Naturalistic fiction often focuses on the harsher realities of life, just like realistic fiction, but it may have a stronger emphasis on the influence of environment and heredity on characters.
You could say 'narrative' or 'fable' are also synonyms for fiction. A narrative is a story or account of events, and a fable is a short fictional tale often with a moral lesson, similar to some types of fiction.
Futuristic fiction. Since a large part of science fiction is set in the future and deals with future societies, technologies, and ways of life, futuristic fiction can be considered a synonym.