Merriam-Webster's Word of the Day for March 27, 2024 is:

auxiliary • \awg-ZILL-yuh-ree\  • adjective

In general use, auxiliary describes someone or something available to provide extra help, power, etc., when it is needed. In linguistics, an auxiliary verb (also called a “helping verb”) is used with another verb to do things like show a verb’s tense or form a question. In nautical contexts, auxiliary can describe a sailboat equipped with a supplementary inboard engine, or a vessel that provides supplementary assistance to other ships.

// The auditorium has an auxiliary cooling system used only on particularly sweltering days.

// “Are” in “They are arriving soon” is an auxiliary verb.

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Examples:

“The popular museum on the National Mall—and its auxiliary Steven F. Udvar-Hazy Center in Chantilly, Virginia—have hundreds of objects on display having to do with flight on Earth, but this will be the first having to do with autonomous flight on another planet.” — Roger Catlin, Smithsonian Magazine, 2 Feb. 2024

Did you know?

What would we do if you sang out of tune—would we stand up and walk out on you? Not likely! Instead, we would provide auxiliary harmonies, joining our voices with yours in support. And if you need a little help from your friends in understanding the meaning of auxiliary, we’re here for that, too—just lend us your ears. Auxiliary, which comes from the Latin noun auxilium, meaning “aid,” “assistance,” or “reinforcement,” is used in a wide range of capacities in English to describe a person or thing that assists another. A fire department may bring in auxiliary units, for example, to battle a tough blaze, or a sailboat may be equipped with an auxiliary engine to supply propulsion when the wind disappears. In grammar, an auxiliary verb assists another (main) verb to express person, number, mood, or tense, such as have in “They have now been informed about the meaning of auxiliary.” Isn’t auxiliary fab?