featherbrained

lacking in seriousness or maturity some featherbrained youngsters giggled through the graduation ceremonies Synonyms birdbrained, ditzy (or ditsy), dizzy, giddy, flighty, frivolous, frothy, futile, goofy, harebrained, light-headed, light-minded, puerile, scatterbrained, silly, yeastyRelated Words fatuous, foolish, inane, nonsensical, thoughtless, witless; crazy, daffy, daft, fruity; exuberant, flippant, fluttery, giggly, happy, light, lighthearted, playful; sappy, shallow, superficialNear Antonyms grave, melancholy, somber (or sombre), thoughtful; dignified, heavy, no-nonsense, sedate, severe, solemn, staidAntonyms earnest, serious, serious-minded, sober, unfrivolous