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.
As they chatted on Discord, a platform favored by videogamers, Brundage was eager to get more information, but he didn’t want to come off as too serious and shut down the conversation.
From The Wall Street Journal • Apr. 3, 2026
Even though Wilkinson counts her experiences with celebrity endorsements and brand deals as being in the business of sales, she found selling real estate to be a much more serious challenge.
From MarketWatch • Apr. 3, 2026
“These were very serious allegations, and we are grateful to the Court for its careful review of the facts, law and voluminous evidence,” they added.
From Los Angeles Times • Apr. 2, 2026
Separately, there have been warnings from DE to schools that they will face "serious challenges" as their budgets will only rise by around 1% in 2026/27.
From BBC • Apr. 1, 2026
“Ida B,” she said, looking at me more serious than ever.
From "Ida B" by Katherine Hannigan
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.
