Direct Opposites:
* Involuntary: This is the most direct opposite and refers to something done without conscious control or choice.
* Compulsory: This emphasizes something being required or enforced, leaving no room for choice.
* Mandatory: Similar to compulsory, this implies something is required by law or regulation.
Other Opposites based on Context:
* Forced: This implies an external pressure or coercion influencing the action.
* Coerced: Similar to forced, but suggests more direct manipulation or pressure.
* Unwilling: This focuses on the lack of desire or enthusiasm for the action.
* Unintentional: This means something was done without conscious intent or purpose.
Example:
If you're talking about a voluntary donation, the opposite might be a compulsory tax.
The best opposite will depend on the specific situation and the nuance you want to convey.