WordReference Random House Learner's Dictionary of American English © 2025
se•ri•ous /ˈsɪriəs/USA pronunciation
adj.
WordReference Random House Unabridged Dictionary of American English © 2025- of or characterized by thought:a serious study of inner-city violence.
- grave, solemn, or somber, as in mood;
not cheerful:He was very serious and didn't even smile. - earnest;
sincere:a serious offer to buy the house. - requiring thought or concentration:serious reading.
- important or significant:Marriage is a serious matter.
- giving cause for worry or fear:a serious relapse.
se•ri•ous
(sēr′ē əs),USA pronunciation adj.
n.
se′ri•ous•ness, n.
- 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.
- giving cause for apprehension;
critical:The plan has one serious flaw. - Medicine(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.
n.
- that which is of importance, grave, critical, or somber:You have to learn to separate the serious from the frivolous.
- Latin sērius or Late Latin sēriōsus; see -ous, -ose1
- late Middle English 1400–50
- 2.See corresponding entry in Unabridged sober, sedate, staid.
- 3.See corresponding entry in Unabridged See earnest 1.
- 5.See corresponding entry in Unabridged momentous, grave.
- 3, 5.See corresponding entry in Unabridged trivial.
'in all seriousness' also found in these entries (note: many are not synonyms or translations):