inscrutable

Merriam-Webster's Word of the Day for October 9, 2026 is:

inscrutable • \in-SKROO-tuh-bul\  • adjective

Inscrutable means "not readily investigated, interpreted, or understood." It often describes things that are mysterious or difficult to comprehend.

// His professor wore an inscrutable expression throughout the oral exam.

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Examples:

"The paper makes significant progress on an unresolved aspect of the inscrutable math equation that determines how the primes are distributed along the number line." — Joseph Howlett, Scientific American, 12 Aug. 2026

Did you know?

Scrutinizing the inscrutable may be futile: even close scrutiny can fail to decipher it. Scrutinizing the scrutable, on the other hand, is likely to yield some understanding. All of these scrut- words have the same Latin root: scrutari, meaning "to search or examine." While scrutiny, scrutinize, and inscrutable all prove themselves useful in everyday discourse, English speakers don’t tend to call much on scrutable, which functions as a synonym of comprehensible.