Inexpugnability could be defined as something that is unable to be defeated or conquered. Some synonyms for this word may include invincibility, indestructibility, impregnability, unbreakability, or immovability. These words all suggest that something is extremely difficult to overcome. For instance, an army with an impregnable fortress may be impossible to conquer without significant resources and effort. Similarly, an indestructible material can withstand extreme force or pressure without being damaged. All of these words convey a sense of strength and power, and they are often used to describe structures, nations, or individuals who are exceptionally resilient or unwavering.