IPA: /ʌnˈpɜːrfəˌmɑːbəl/
KK: /ʌnˈpɜrˌfɔr.mə.bəl/
Something that cannot be done or carried out.
The task was deemed unperformable due to its complexity.
Unperformable → It is formed from "un-" (meaning not) and "perform" (from Latin "performare", meaning to carry out or accomplish) and "-able" (meaning capable of). The word "unperformable" means not capable of being carried out or accomplished.
Think of 'not' ('un-') being able to 'carry out' ('perform') a task, which is why 'unperformable' means something that cannot be accomplished.