frivolous
friv-o-lous
adjective
Lacking seriousness or importance; silly and not sensible.
"Don't waste time on such frivolous matters."
Thesaurus
Synonyms: idle, airheaded, trivial, flyaway, dizzy, scatterbrained, featherbrained, lightheaded, flighty, light, flippant, light-headed
Antonyms: serious