The concept of not being assailable refers to something that is not easily attacked or defeated. This can be achieved by various means, such as strength, defense, and protection. Some synonyms that can be used to replace the term not assailable include invincible, impregnable, unbreakable, unconquerable, impervious, and sturdy. Each of these words denotes something that is difficult to overcome, whether it is physical or metaphorical. They can be utilized in different contexts to express a similar meaning to not assailable. These synonyms are useful for enhancing written or spoken language and conveying a sense of security, resilience, and robustness.