1
: having an important or dangerous possible result
a serious injury/illness/condition
"You sound terrible." "It's just a bad cold. Nothing serious."
serious risks
For my brother, not going to college was a serious mistake.
Crime is a serious problem in this neighborhood.
2
: involving or deserving a lot of thought, attention, or work
a serious study
The team is a serious contender for the championship.
If you want to quit smoking, you have to make a serious effort.
They had a serious conversation about their relationship.
a serious novel about modern life
The story raises serious questions about our system of justice.
Dog shows are a serious business.
3
: giving a lot of attention or energy to something
serious musicians
She is a serious cyclist who rides 200 miles each week.
Serious journalists do not pry into the personal lives of famous people.
When it comes to fishing, he's very serious. = He's very serious about fishing.
My sister is serious about her grades.
4
: not joking or funny
a serious story/opera
Don't laugh. I'm serious!
Can you be serious just this once? This is important.
He is serious about moving down South. [=he truly wants/intends to move down South]
"He says he won't do it." "Are you serious?"
"I'm joining the army." "You can't be serious." [=you have to be joking; I can't believe that you're really joining the army]
5
always used before a noun informal
: large or impressive in quality or amount
After business school, he started making some serious money. [=he started making a large amount of money]
These are serious shoes!
They did some serious drinking at the bar. [=they drank a lot]
6
: having or involving strong romantic feelings
Their romance is quite serious. They're even talking about marriage.
We've dated a few times, but it's nothing serious.
They are a serious couple.
He's never really had a serious relationship with a woman.
—often + aboutShe and her boyfriend are serious about each other.
7
: thoughtful or quiet in appearance or manner
He looks like a serious person.
You look serious. What's the matter?
Cite this Entry
“Serious.” Merriam-Webster.com Simple Definition, Merriam-Webster, https://www.merriam-webster.com/simple/serious. Accessed 25 Apr. 2026.
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