Direct opposites:
* Unwilling: This is the most direct opposite, meaning not wanting to do something.
* Reluctant: This implies hesitation or resistance to doing something.
Other possibilities:
* Averse: This suggests a strong dislike or aversion to something.
* Resistant: This implies a strong opposition to something.
* Hesitant: This suggests uncertainty or doubt about doing something.
* Refusing: This indicates a clear and definite rejection of something.
The best antonym for "willing" depends on the specific situation and the nuance you want to convey.