[adj] absent-mindedly irresponsible; "he said I was too flighty to be a good supervisor" [adj] lacking sense or discretion; "his rattlebrained crackpot ideas"; "how rattlepated I am! I've forgotten what I came for"- Glenway Westcott
flighty, foolish, head-in-the-clouds, irresponsible, rattlebrained, rattlepated, scatty