characterized by lack of seriousness or sense

frivolous conduct.

self-indulgently carefree; unconcerned about or lacking any serious purpose.

(of a person) given to trifling or undue levity

a frivolous, empty-headed person.

of little or no weight, worth, or importance; not worthy of serious notice

a frivolous suggestion.

adjective

grave , mature , sensible , serious , solemn , thoughtful , wise

adjective

barmy * , childish , dizzy * , empty-headed * , facetious , featherbrained * , flighty , flip , flippant , foolish , gay , giddy * , harebrained * , idiotic , idle , ill-considered , impractical , juvenile , light , light-minded , minor , niggling * , nonserious , not serious , paltry , peripheral , petty , playful , pointless , puerile , scatterbrained * , senseless , shallow , sportive , superficial , tongue-in-cheek * , unimportant , unprofound , volatile , whimsical , empty-headed , featherbrained , frothy , harebrained , lighthearted , scatterbrained , silly , carefree , childlike , fribble , frolicsome , futile , giddy , hoity-toity , inane , inconsequential , insignificant , irrelevant , trifling , trivial , worthless , yeasty