Merriam-Webster's Word of the Day for September 18, 2025 is:

rationale • \rash-uh-NAL\  • noun

Rationale refers to an explanation or reason for something said or done. It is often used with for, behind, or of.

// City council members who oppose the zoning change should be ready to explain their rationale for voting against it.

// She’s explained the rationale behind her early retirement.

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Examples:

“There is a rationale for commercializing seagrass production, but ecologically sustainable production needs to be at the heart of that business model, and the numbers for doing that simply don’t add up at the moment.” — Richard Lilley, quoted in Smithsonian Magazine, 7 Oct. 2024

Did you know?

If someone asserts that the word rationale refers to a ration of ale, they are wrong, but that doesn’t mean they don’t have an actual rationale (a reason, explanation, or basis) for such a claim. “Rationale looks like the words ration and ale jammed together,” they could offer, and while that is true you’d be justified in responding: “Appearances can be deceiving.” Rationale is a direct borrowing of the Latin word rationale, with which it shares the meaning “an explanation of controlling principles of opinion, belief, practice, or phenomena.” The Latin rationale comes from a form of the adjective rationalis (“rational”), which traces back to the noun ratio, meaning “reason.” While the Latin ratio is also the forebear of the English noun ration, referring to a share of something, rationale has nothing to do with a tankard (or stein, or even a pony) of beer.