What prefix must be added to poisonous?

The prefix you can add to "poisonous" depends on the meaning you want to convey. Here are some options:

For making something more poisonous:

* Hyper-: Hyperpoisonous means extremely poisonous.

* Super-: Superpoisonous means highly poisonous, surpassing others in toxicity.

For indicating a connection to poison:

* Anti-: Antipoisonous means resistant to poison or counteracting its effects.

* Pseudo-: Pseudopoisonous means mimicking the effects of poison, but not actually poisonous.

* Toxic-: Toxicpoisonous emphasizes the inherent toxicity of something.

For emphasizing the nature of the poison:

* Bio-: Biopoisonous means poisonous due to biological origins.

* Chemo-: Chemopoisonous means poisonous due to chemical properties.

The best prefix to use will depend on the specific context and the intended meaning.