Open English Wordnet
Adjectives
(s)rattlebrained, rattlepated, scatterbrained, scattylacking sense or discretion“his rattlebrained crackpot ideas”, “how rattlepated I am! I've forgotten what I came for” (Glenway Westcott)
(s)flighty, flyaway, head-in-the-clouds, scatterbrainedguided by whim and fancy“flighty young girls”