Unfathomable/ʌnˈfæðəməbl/ Definition 1 of 2Pro Tip 1/3Abstract Concepts Use 'unfathomable' to describe complex ideas or things not easily measured or understood. The concept of infinity is unfathomable to many. Pro Tip 2/3Emotional Impact 'Unfathomable' can express a strong emotional response to the vastness or complexity of something. Her kindness was truly unfathomable. Pro Tip 3/3Hyperbolic Usage Sometimes used to exaggerate for dramatic effect, not to be taken literally. He had an unfathomable amount of homework.