serious

1 not joking or playful in mood or manner I'm serious when I say that no one should be walking in that neighborhood at night Synonyms earnest, grave, humorless, no-nonsense, po-faced [British], sedate, severe, sober, sobersided, solemn, staid, uncomic, unsmiling, weighty Related Words harsh, stern, strict; businesslike, professional; dignified, distinguished, elevated, serious-minded; gloomy, grim Near Antonyms antic, comic, comical, droll, farcical, funny, hilarious, hysterical (also hysteric), laughable, light, light-headed, ludicrous, ridiculous, riotous, risible, screaming, sidesplitting, uproarious; featherbrained, flighty, frivolous, goofy, harebrained, lighthearted, puerile, scatterbrained; absurd, asinine, balmy, brainless, cockeyed, crazy, cuckoo, daffy, daft, dotty, fatuous, foolish, half-witted, insane, jerky, kooky (also kookie), loony (also looney), lunatic, mad, nonsensical, nutty, preposterous, sappy, screwball, senseless, silly, unwise, wacky (also whacky), weak-minded, witless, zany Antonyms facetious, flip, flippant, humorous, jesting, jocular, joking, kittenish, ludic, playful

2 having a matter of importance as its topic a very serious film that dealt with the aftermath of the Gulf War Synonyms grave, heavy, weighty Related Words big, consequential, eventful, important, major, material, meaningful, momentous, portentous, significant, solid, substantial Near Antonyms frivolous, insignificant, lite, little, Mickey Mouse, minor, silly, slight, small, trivial, unimportant Antonyms light, unserious

3 involving potential loss or injury a serious accident Synonyms grave, grievous, hazardous, jeopardizing, menacing, parlous, perilous, risky, dangerous, threatening, unhealthy, unsafe, venturesomeRelated Words dicey, insecure, precarious, treacherous, uncertain; ultrahazardous; chance, haphazard, random; distressing, sickening, unpleasant; ugly, wicked; adverse, bad, baleful, baneful, deleterious, detrimental, evil, harmful, hurtful, ill, inimical, injurious, malignant, nasty, noxious, pernicious, pestilent; deadly, deathly, destructive, dire, fatal, fateful, fell, killer, lethal, mortal, murderousNear Antonyms advantageous, beneficial, good; ultrasafeAntonyms harmless, innocent, innocuous, nonhazardous, nonthreatening, safe, unthreatening