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.
Kennedy sought the advice of doctors after dealing with severe memory loss and brain fog, reportedly leading to a scan of his brain that showed a dark spot in the imagery. Angel Saunders, PEOPLE, 15 Oct. 2025 During perimenopause, the decline in estrogen —which Noble explains as not just a hormone, but a neuroendocrine transmitter that helps the brain stay alert and energized—triggers the brain fog and can affect a variety of cognitive functions depending on the individual. Alexa Mikhail, Flow Space, 14 Oct. 2025 There’s brain fog in there too. Nick Caruso, TVLine, 2 Oct. 2025 The one who fights brain fog and exhaustion all day? Alyce Collins, MSNBC Newsweek, 19 Sep. 2025 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

Browse Nearby Words

Cite this Entry

“Brain fog.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/brain%20fog. Accessed 21 Oct. 2025.

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)
Last Updated: - Updated example sentences
Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!