What is another word for rock-hard?
Pronunciation: [ɹˈɒkhˈɑːd] (IPA) 
When describing an object or material that is exceptionally firm and hard, the phrase "rock-hard" is often used. However, there are numerous other synonyms that can be used in place of this expression. Some of the commonly used synonyms include impenetrable, solid, unyielding, unbreakable, unshakable, and unflinching. Other words that are applicable for describing something that is exceptionally hard include unrelenting, firm, stout, unassailable, immoveable, and unyielding. These words convey the idea of an object or material being firm and resistant to any kind of wear and tear. So, you have many options to choose from when you want to describe hardness, and "rock-hard" is just one of them.
