General opposites:
* Useless: This is the most direct opposite, meaning not helpful or beneficial.
* Futile: Implying something is pointless or ineffective.
* Worthless: Lacking value or significance.
* Harmful: Causing damage or negative effects.
* Ineffective: Failing to achieve the desired result.
Specific opposites based on context:
* Harmful: If "useful" means beneficial, the opposite could be harmful.
* Unnecessary: If "useful" means needed, the opposite could be unnecessary.
* Redundant: If "useful" means unique and essential, the opposite could be redundant.
* Impractical: If "useful" means practical, the opposite could be impractical.
To choose the best opposite word, consider the specific situation and what aspect of "useful" you want to contrast.