serious
Americanadjective
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of, showing, or characterized by deep thought.
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of grave or somber disposition, character, or manner.
a serious occasion; a serious man.
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being in earnest; sincere; not trifling.
His interest was serious.
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requiring thought, concentration, or application.
serious reading; a serious task.
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weighty or important.
a serious book; Marriage is a serious matter.
- Antonyms:
- trivial
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giving cause for apprehension; critical.
The plan has one serious flaw.
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Medicine/Medical. (of a patient's condition) having unstable or otherwise abnormal vital signs and other unfavorable indicators, as loss of appetite and poor mobility: patient is acutely ill.
noun
adjective
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grave in nature or disposition; thoughtful
a serious person
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marked by deep feeling; in earnest; sincere
is he serious or joking?
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concerned with important matters
a serious conversation
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requiring effort or concentration
a serious book
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giving rise to fear or anxiety; critical
a serious illness
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informal worthy of regard because of substantial quantity or quality
serious money
serious wine
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informal extreme or remarkable
a serious haircut
Related Words
See earnest 1.
Other Word Forms
- half-serious adjective
- half-seriously adverb
- nonserious adjective
- nonseriously adverb
- overserious adjective
- overseriously adverb
- quasi-serious adjective
- quasi-seriously adverb
- seriousness noun
- superserious adjective
- superseriously adverb
- ultraserious adjective
- ultraseriously adverb
- unserious adjective
- unseriously adverb
Etymology
Origin of serious
First recorded in 1400–50; late Middle English, from Middle French serieux and Latin sērius “grave, earnest” or Late Latin sēriōsus; -ous, -ose 1
Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
That includes a bill of more than £616m to fix the most serious issues at 12 of Wales' 13 main hospitals.
From BBC • Apr. 2, 2026
Baldoni lawyers Alexandra Shapiro and Jonathan Bach said they were grateful for the dismissal of the “very serious allegations,” adding, “What’s left is a significantly narrowed case.”
From The Wall Street Journal • Apr. 2, 2026
One patient required treatment for hemolytic uremic syndrome, a serious kidney complication.
From Los Angeles Times • Apr. 2, 2026
Read on: These stocks are ‘the place to be’ if you want serious AI growth, says BofA.
From MarketWatch • Apr. 1, 2026
His hands were shoved down in his pockets and he had a serious look on his face.
From "Summer of the Monkeys" by Wilson Rawls
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
