1. Grave in quality or manner: gave me a serious look.
2. 1. Carried out in earnest: engaged in serious drinking; serious study of Italian.
   2. Deeply interested or involved: a serious card player.
   3. Designed for and addressing grave and earnest tastes: serious art; serious music.
   4. Not trifling or jesting: I'm serious: we expect you to complete the assignment on time. Her question was serious enough to deserve a thoughtful response.
   5. Informal Of considerable size or scope; substantial: a cleanup that cost serious money.
   6. Of such character or quality as to appeal to the expert, the connoisseur, or the sophisticate: "Every serious kitchen needs at least one peppermill" (Washington Post).
   7. Being of such import as to cause anxiety: serious injuries; a serious turn of events.
   8. Too complex to be easily answered or solved: raised some serious objections to the proposal.
3. Concerned with important rather than trivial matters: a serious student of history.
4. 1. Being of such import as to cause anxiety: serious injuries; a serious turn of events.
   2. Too complex to be easily answered or solved: raised some serious objections to the proposal.

Synonyms: 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 opposed to play: serious students of music.
Sober emphasizes circumspection and self-restraint: "My sober mind was no longer intoxicated by the fumes of politics" (Edward Gibbon).
Grave suggests the dignity and somberness associated with weighty matters: "a quiet, grave man, busied in charts, exact in sums, master of the art of tactics" (Walter Bagehot).
Solemn often adds to grave the suggestion of impressiveness: the judge's solemn tone as she handed down her decision.
Earnest implies sincerity and intensity of purpose: disputants who showed an earnest desire to reach an equitable solution.
Sedate implies a composed, dignified manner: "One of those calm, quiet, sedate natures, to whom the temptations of turbulent nerves or vehement passions are things utterly incomprehensible" (Harriet Beecher Stowe).
Staid emphasizes dignity and an often strait-laced observance of propriety: "a grave and staid God-fearing man" (Tennyson).