Synonyms for Not serious:

• adj.

  •facetious (adjective)
  • humorous,
  • merry,
  • amusing,
  • blithe,
  • jocose,
  • Capering,
  • smart,
  • sarcastic,
  • jesting,
  • waggish,
  • pleasant,
  • comical,
  • sprightly,
  • funny,
  • indecorous,
  • whimsical,
  • clever,
  • fanciful,
  • droll,
  • dry,
  • jocular,
  • comic,
  • ridiculous,
  • flippant,
  • joshing,
  • satirical,
  • gay,
  • flip.
  •frivolous (adjective)
  • paltry,
  • unimportant,
  • harebrained,
  • dizzy,
  • childish,
  • niggling,
  • giddy,
  • foolish,
  • pointless,
  • tongue-in-cheek,
  • juvenile,
  • minor,
  • puerile,
  • scatterbrained,
  • featherbrained,
  • superficial,
  • idiotic,
  • peripheral,
  • light,
  • senseless,
  • volatile,
  • impractical,
  • petty,
  • empty-headed,
  • barmy.
  •idle (adjective)
  • groundless,
  • bootless,
  • nugatory,
  • futile,
  • insignificant,
  • unnecessary,
  • fruitless,
  • rambling,
  • vain,
  • empty,
  • useless,
  • unsuccessful,
  • otiose,
  • unavailing,
  • unproductive,
  • abortive,
  • hollow.
  •pardonable (adjective)
  • venial.
  •tongue-in-cheek (adjective)
  • kiddingly,
  • in jest,
  • ironical,
  • in fun,
  • jokingly,
  • tongue in cheek.
  •venial (adjective)
  • forgivable,
  • tolerable,
  • okay,
  • permissible,
  • excusable,
  • slight,
  • defensible,
  • all right,
  • not too bad,
  • understandable,
  • allowable,
  • justifiable,
  • explainable.

• Other synonyms:

  •adj.
  • facetious,
  • farcical,
  • flighty,
  • idler,
  • ill-considered,
  • ironic,
  • irrelevant,
  • irreverent,
  • joking,
  • laughable,
  • light-minded,
  • ludicrous,
  • playful,
  • salty,
  • shallow,
  • sportive,
  • trivial,
  • witty,
  • wry,
  • shallower,
  • funnier,
  • nonserious,
  • unprofound,
  • flipper,
  • frivolous,
  • idle,
  • punning,
  • unhelpful,
  • putting one on,
  • wisecracking,
  • emptyheaded,
  • of no avail,
  • pulling one's leg.

Antonyms for Not serious:

• adj.

  • facetious
    grave, formal, unfunny, serious.
  • frivolous
    sensible, solemn, intelligent, thoughtful, mature, wise.
  • idle
    diligent, important, worthwhile, Hustling, used, busy, effective, employed, productive, active, working, ambitious.
  • tongue-in-cheek
    respectful, reverent.