1 childish, ditsy (U.S. informal) dizzy, empty-headed, flighty, flip (informal) flippant, foolish, giddy, idle, ill-considered, juvenile, light-minded, nonserious, puerile, silly, superficial
2 extravagant, footling (informal) impractical, light, minor, nickel-and-dime (U.S. slang) niggling, paltry, peripheral, petty, pointless, shallow, trifling, trivial, unimportant
Antonyms
earnest, important, mature, practical, responsible, sensible, serious, solemn, vital