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.
The study shows that aging lung cells can trigger an overly aggressive immune response, which can turn even mild infections into serious conditions.
From Science Daily • Apr. 3, 2026
My colleague, Charles McNulty, has alerted us to the serious problems facing theater in L.A.
From Los Angeles Times • Apr. 3, 2026
To understand the fascination, two sociologists spoke to more than 160 "Bigfooters" who are serious about collecting evidence that the beast is real.
From BBC • Apr. 3, 2026
Several countries have enacted anti-cyberscam laws to combat the rise of online fraud, romance and cryptocurrency scams, with con artists in Singapore facing 24 strokes of the cane for serious cases.
From Barron's • Apr. 3, 2026
A newscaster appeared beside the photo and spoke with a serious frown on her face.
From "The Way to Rio Luna" by Zoraida Cordova
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.
