adj. 25B6; adjective
a frivolous girl : SKITTISH, flighty, giddy, silly, foolish, superficial, shallow, light-minded, irresponsible, thoughtless, feather-brained, empty-headed, pea-brained, birdbrained, vacuous, vapid; informal dizzy, dippy; N. Amer. informal ditzy.
frivolous remarks : FLIPPANT, glib, facetious, joking, jokey, light-hearted; fatuous, inane, senseless, thoughtless; informal flip.
new rules to stop frivolous lawsuits : TIME-WASTING, pointless, trivial, trifling, minor, petty, insignificant, unimportant.
sensible, serious.