birdbrained, birdwitted, brainless, capricious, dizzy, empty-headed, featherheaded, fickle, flighty, fluffy, fluttery, frivolous, frothy, gaga, giddy-brained, giddy-headed, giddy-pated, giddy-witted, giddy, harebrain, harebrained, impulsive, light, rattlebrained, rattleheaded, rattlepated, scatterbrained, scramblebrained, shallow-headed, shallow-minded, shallow-pated, shallow-witted, shallow, shatterbrained, silly, skittish, superficial, thoughtless, unprofound, volatile, whimsical, witless