serious, grave, solemn, sedate, staid, sober, earnest mean not light or frivolous. serious implies a concern for what really matters.

Please don't laugh - I'm being serious. He was wearing a very serious expression and I knew something was wrong. On the surface it's a very funny novel but it does have a more serious underlying theme.

SERIOUS definition: of, showing, or characterized by deep thought. See examples of serious used in a sentence.

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 …

Any important situation is serious, and this word is also the opposite of humorous and playful.

If someone is serious about something, they are sincere about what they are saying, doing, or intending to do. You really are serious about this, aren't you?

Feb 21, 2026 · Adjective serious (comparative more serious, superlative most serious) Without humor or expression of happiness; grave in manner or disposition.

• If you are serious about meeting your goals, telling the world in clear and certain terms will help you meet them. • The tabloids would never describe themselves as completely serious but we are …

These adjectives refer to manner, appearance, disposition, or acts marked by absorption in thought, pressing concerns, or significant work. Serious implies a concern with responsibility and work as …

Definition of serious adjective in Oxford Advanced Learner's Dictionary. Meaning, pronunciation, picture, example sentences, grammar, usage notes, synonyms and more.