serious
Americanadjective
-
of, showing, or characterized by deep thought.
-
of grave or somber disposition, character, or manner.
a serious occasion; a serious man.
-
being in earnest; sincere; not trifling.
His interest was serious.
-
requiring thought, concentration, or application.
serious reading; a serious task.
-
weighty or important.
a serious book; Marriage is a serious matter.
- Antonyms:
- trivial
-
giving cause for apprehension; critical.
The plan has one serious flaw.
-
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
-
grave in nature or disposition; thoughtful
a serious person
-
marked by deep feeling; in earnest; sincere
is he serious or joking?
-
concerned with important matters
a serious conversation
-
requiring effort or concentration
a serious book
-
giving rise to fear or anxiety; critical
a serious illness
-
informal worthy of regard because of substantial quantity or quality
serious money
serious wine
-
informal extreme or remarkable
a serious haircut
Synonym Usage
See earnest 1.
Other Word Forms
-
seriousnessnoun
-
half-seriousadjective
-
nonseriousadjective
-
overseriousadjective
-
quasi-seriousadjective
-
superseriousadjective
-
ultraseriousadjective
-
unseriousadjective
-
half-seriouslyadverb
-
nonseriouslyadverb
-
overseriouslyadverb
-
quasi-seriouslyadverb
-
superseriouslyadverb
-
ultraseriouslyadverb
-
unseriouslyadverb
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; see -ous, -ose 1
Explanation
Any important situation is serious, and this word is also the opposite of humorous and playful. If you're frowning, someone might say, "Why so serious?" This is a word for people and situations where there's no fooling around. If you're staring at the computer screen, typing quickly, you look serious. If you are in a car accident, that's a serious situation. Some people are more serious than others. If you're always making jokes and smiling, then you're not that serious. One place everyone needs to be serious is at a funeral home.
Vocabulary lists containing serious
The SAT: Words to Capture Tone, List 3
Looking to grow your vocabulary? Check out this interactive, curated word list from our team of English language specialists at Vocabulary.com – one of over 17,000 lists we've built to help learners worldwide!
The SAT: Multiple-Meaning Words, List 5
Interested in learning more words like this one? Our team at Vocabulary.com has got you covered! You can review flashcards, quiz yourself, practice spelling, and more – and it's all completely free to use!
The New SAT: Words to Capture Tone
Want to remember this word for good? Start your learning journey today with our library of interactive, themed word lists built by the experts at Vocabulary.com – we'll help you make the most of your study time!
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.
"I also pay tribute to the rail staff, emergency services and those in the community who responded to this serious incident."
From BBC • Jun. 23, 2026
Attorney Daniel Rosen simply said that “is not the measure of whether or not they committed a serious federal crime.”
From Salon • Jun. 23, 2026
“Families are still dealing with the smoke, odor, ash, closed parks and community spaces, disrupted routines and serious concerns about what they are breathing. And people are tired, they are anxious, and they deserve answers.”
From Los Angeles Times • Jun. 23, 2026
The incumbents recognize a serious threat when they see one.
From The Wall Street Journal • Jun. 23, 2026
A childcare business is way more serious, though.
From "South of Somewhere" by Kalena Miller
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.
