brain fog

noun

: a usually temporary state of diminished mental capacity marked by inability to concentrate or to think or reason clearly

Examples of brain fog in a Sentence

Recent Examples on the Web
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
But many live with fatigue, weakness, brain fog and other symptoms for months or years before a deficiency is caught. — Amanda Schupak, CNN Money, 23 Oct. 2026 For example, brain fog and fatigue are common with MS but also a number of other conditions. — Helen Carefoot, Flow Space, 21 Oct. 2026 Men with low testosterone after a head injury often report lack of energy, fatigue, low libido or brain fog, Lockette said, and sports concussions are frequently overlooked as a cause. — Samantha Agate, Kansas City Star, 19 Oct. 2026 Among the most common are hot flashes, depression, genital and urinary symptoms, brain fog and other neurological symptoms, and skin and hair issues. — Maggie Astor, New York Times, 15 Oct. 2026 See All Example Sentences for brain fog

Word History

First Known Use

1853, in the meaning defined above

Time Traveler
The first known use of brain fog was in 1853

Rhymes for brain fog

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Browse Nearby Words

brain-fever bird
brain fog
brain food
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Cite this Entry

“Brain fog.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/brain%20fog. Accessed 27 Oct. 2026.

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Medical Definition

brain fog

noun
: a usually temporary state of diminished mental capacity marked by inability to concentrate or to think or reason clearly
This brain fog can be a result of being overly stressed, tired, carrying extra weight, consuming too many calories or consistently consuming a diet poor in nutrients.—Kylie Helgens, The Gazette (Cedar Rapids, Iowa)
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