1. of, showing, or characterized by deep thought.
  2. of grave or somber disposition, character, or manner: a serious occasion; a serious man.
  3. being in earnest; sincere; not trifling: His interest was serious.
  4. requiring thought, concentration, or application: serious reading; a serious task.
  5. weighty or important: a serious book; Marriage is a serious matter.
  6. giving cause for apprehension; critical: The plan has one serious flaw.
  7. Medicine/Medical. (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.
  1. that which is of importance, grave, critical, or somber: You have to learn to separate the serious from the frivolous.

Origin of serious

1400–50; late Middle English < Latin sērius or Late Latin sēriōsus; see -ous, -ose1
Related formsse·ri·ous·ness, nounhalf-se·ri·ous, adjectivehalf-se·ri·ous·ly, adverbhalf-se·ri·ous·ness, nounnon·se·ri·ous, adjectivenon·se·ri·ous·ly, adverbnon·se·ri·ous·ness, nouno·ver·se·ri·ous, adjectiveo·ver·se·ri·ous·ly, adverbo·ver·se·ri·ous·ness, nounqua·si-se·ri·ous, adjectivequa·si-se·ri·ous·ly, adverbsu·per·se·ri·ous, adjectivesu·per·se·ri·ous·ly, adverbsu·per·se·ri·ous·ness, nounul·tra·se·ri·ous, adjectiveul·tra·se·ri·ous·ly, adverbul·tra·se·ri·ous·ness, nounun·se·ri·ous, adjectiveun·se·ri·ous·ly, adverbun·se·ri·ous·ness, noun

Synonyms for serious

2. sober, sedate, staid. 3. See earnest1. 5. momentous, grave.

Antonyms for serious

3, 5. trivial. Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for half serious


  1. grave in nature or disposition; thoughtfula serious person
  2. marked by deep feeling; in earnest; sincereis he serious or joking?
  3. concerned with important mattersa serious conversation
  4. requiring effort or concentrationa serious book
  5. giving rise to fear or anxiety; criticala serious illness
  6. informal worthy of regard because of substantial quantity or qualityserious money; serious wine
  7. informal extreme or remarkablea serious haircut
Derived Formsseriousness, noun

Word Origin for serious

C15: from Late Latin sēriōsus, from Latin sērius; probably related to Old English swǣr gloomy, Gothic swers esteemed
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for half serious



mid-15c., "expressing earnest purpose or thought" (of persons), from Middle French sérieux "grave, earnest" (14c.), from Late Latin seriosus, from Latin serius "weighty, important, grave," probably from a PIE root *swer- (4) "heavy" (cf. Lithuanian sveriu "to weigh, lift," svarus "heavy;" Old English swære "heavy," German schwer "heavy," Gothic swers "honored, esteemed," literally "weighty"). As opposite of jesting, from 1712; as opposite of light (of music, theater, etc.), from 1762. Meaning "attended with danger" is from 1800.

Online Etymology Dictionary, © 2010 Douglas Harper

half serious in Medicine


  1. Being of such import as to cause anxiety, as of a physical condition.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.