Merriam-Webster's Word of the Day for October 9, 2026 is "inscrutable." Inscrutable is an adjective meaning something is not easily investigated, interpreted, or understood. It is often used to describe things that are mysterious or hard to comprehend. For instance, a professor might have an inscrutable expression during an exam. The word can apply to complex concepts, like an inscrutable math equation. The Latin root for this word is "scrutari," meaning to search or examine. Words like "scrutiny" and "scrutinize" share this root and involve careful examination. While "scrutiny" and "scrutinize" are common, "scrutable" is less frequently used. "Scrutable" means comprehensible, the opposite of inscrutable. Therefore, scrutinizing something inscrutable might not lead to understanding.