The Collaborative International Dictionary of English v.0.48:
Rattle-brained \Rat"tle-brained`\ (r[a^]t"t'l*br[=a]nd`), a. Giddy; rattle-headed. [1913 Webster]WordNet (r) 3.0 (2006):
rattlebrained adj 1: lacking sense or discretion; "his rattlebrained crackpot ideas"; "how rattlepated I am! I've forgotten what I came for"- Glenway Westcott [syn: rattlebrained, rattlepated, scatterbrained, scatty]