Describing something in a way that makes it sound less significant than it really is can best be called?

The term that best describes the act of portraying something as less significant than it truly is known as understatement. Understatement is a rhetorical device often used to emphasize a point by intentionally presenting it in a restrained manner. For example, saying "It’s just a scratch" when referring to a large dent in a car can highlight the severity of the damage through the apparent minimization of its importance.

In contrast, the other terms listed have distinct meanings. A metaphor involves comparing two unlike things directly for effect, hyperbole refers to exaggerated statements not meant to be taken literally, and synecdoche refers to a figure of speech where a part represents the whole or vice versa. Understanding these distinctions clarifies why understatement is the most fitting term for describing the minimizing of significance.