Merriam-Webster's Word of the Day for December 22, 2022 is: deleterious \del-uh-TEER-ee-us\ adjective

Deleterious is a word used in formal speech and writing to describe something that is damaging or harmful, usually in a subtle or unexpected way.

// While the popular lawn care product is effective at eliminating weeds, it unfortunately is also deleterious to the wider environment.

[See the entry >](https://www.merriam-webster.com/dictionary/deleterious)

Examples:

“[Margo Jefferson’s] award-winning memoir, ‘Negroland’ (2015), describes the comic moments and deleterious effects that come with maintaining the codes of and being raised within the paradisiacal confines of Black [bourgeois](https://www.merriam-webster.com/dictionary/bourgeois) life in Chicago at midcentury.” — Walter Muyumba, The Boston Globe, 14 Apr. 2022

Did you know?

When you hold down the delete key on your keyboard or touchscreen, the effect—whoosh!—is instantaneous (unless your device is [laggy](https://www.merriam-webster.com/dictionary/laggy), of course). Deleterious effects, however, are often not so obvious; deleterious is used to describe things that are harmful in ways that are unexpected, slow-acting, or not readily apparent. Although most often used in formal speech and writing, deleterious is far from rare. It even pops up from time to time in film and television, especially from the mouths of [wonky](https://www.merriam-webster.com/dictionary/wonky#h1) characters, as when Seven of Nine warns the Doctor in an episode of Star Trek Voyager, “The nebula is having a deleterious effect on all the ship’s technology,” or when Higgins exclaims in the original Magnum P.I. series, “It’s shocking what a deleterious effect a regimen of nothing but mushrooms can have on a man.” We’ll take your word for it, Higgins.