General synonyms:
* Inspiration: This is the most general and common synonym.
* Stimulus: Something that encourages creativity or thought.
* Influence: A person or thing that has a significant impact on someone's work.
More specific synonyms:
* Patron: A person who supports an artist financially or otherwise.
* Patroness: A female patron.
* Model: Someone who serves as a subject for an artist.
* Subject: The topic or theme of a work of art.
* Source of inspiration: Something that provides the spark for creativity.
Figurative synonyms:
* Spirit: A guiding force or influence.
* Genius: Exceptional mental ability or creativity.
* Ethereal being: A supernatural or idealized entity.
The best synonym for "muse" will depend on the specific situation and the intended meaning.