1. Thoughtful, somber, or grave in manner: He became serious when he was asked about the economy.
2. Not joking or trifling: I was serious when I said I liked your haircut.
3. Deeply interested or involved: a serious golfer.
4. Meriting great concern: a serious illness; a serious mistake.
5. Performed with careful thought: a serious effort to reform tax policy.
6. Pertaining to important rather than trivial matters: a serious discussion.
7. Sincerely meant: mistook a sarcastic comment for a serious question.
8. Intended for sophisticated people: serious music.
9. Informal Of considerable size or scope; substantial: a serious amount of money.
[Middle English, from Old French serieux, from Late Latin sēriōsus, from Latin sērius.]
Synonyms: serious, sober, grave2, solemn, earnest1
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: "When ... his sober demeanor gave way at the graveside, it was with the severity of one bereft beyond redemption" (Philip Roth).
Grave suggests the dignity and somberness associated with weighty matters: "a little girl with brownish-blackish hair standing at one of those windows like a grave captain at the prow of a ship" (Stacey D'Erasmo).
Solemn often adds to grave the suggestion of impressiveness: The judge was solemn when issuing the sentence. Earnest implies sincerity and intensity of purpose: We are earnest in our desire to reach an equitable solution.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.