Iron-hard is a descriptive term used to depict an object or substance that is extremely hard, tough, and durable. However, there are several alternative words that can be used instead of iron-hard to convey a similar meaning. Some of these synonyms include "adamant," "unyielding," "solid," "sturdy," "indestructible," "unbreakable," and "resilient." Each of these words represents the type of strength and durability that is similar to that of iron. Therefore, it is important to choose the appropriate synonym that best suits the context in which it is being used.