Unpierceable is a word that refers to something that cannot be pierced or penetrated. There are various synonyms that can be used to replace this word and still convey the same meaning. One of these synonyms is impenetrable, which means impossible to penetrate or pass through. Other synonyms include indestructible, invulnerable, unbreakable, and impervious. Each of these words implies an object, material or surface that cannot be damaged or pierced by external force or impact. Whether you choose to use the word unpierceable or any of its synonyms, the message remains the same, describing something that cannot be pierced.