General:
* Extinct - This is the most direct and common adjective, meaning something no longer exists.
* Vanished - Implies a complete disappearance.
* Gone - Similar to vanished, but simpler and less formal.
Specific to species:
* Endangered - Refers to a species at risk of extinction.
* Threatened - Similar to endangered, but may have a slightly less severe connotation.
* Critically endangered - A species facing an extremely high risk of extinction.
* Extinct in the wild - A species that only exists in captivity.
Other related adjectives:
* Lost - Can refer to the loss of a species or a specific feature.
* Irrecoverable - Indicates that something cannot be restored or brought back.
* Doomed - Suggests a certain fate of extinction.
The best choice will depend on the specific context and the desired nuance.