nonserious

foolish idiotic impractical petty pointless senseless

barmy childish dizzy empty-headed facetious featherbrained flighty flip flippant gay giddy harebrained idle ill-considered juvenile light light-minded minor niggling not serious paltry peripheral playful puerile scatterbrained shallow sportive superficial tongue-in-cheek unimportant unprofound volatile whimsical

intelligent sensible wise

grave mature serious solemn thoughtful