23 synonyms for unavoidable such as certain, assured, and bound/sure to happen. Unavoidable is an adjective, and its antonyms are avoidable and preventable.
Assured, bound/sure to happen, certain, compulsory, fated, for sure, ineluctable, ineludible, inescapable, inevitable, inexorable, mandatory, necessary, obligatory, out of one's hands, predestined, predetermined, preordained, prescribed, required, sure, and unpreventable.