lacking sense or discretion; "his rattlebrained crackpot ideas"; "how rattlepated I am! I've forgotten what I came for"- Glenway Westcott
lost in thought; showing preoccupation; "an absent stare"; "an absentminded professer"; "the scatty glancing quality of a hyperactive but unfocused intelligence"
{s} not thinking in a clear and orderly manner, heedless, scatterbrained (British Slang)
If you describe someone as scatty, you mean that they often forget things or behave in a silly way. Her mother is scatty and absent-minded. = scatterbrained. someone who is scatty often forgets or loses things because they are not sensible or practical (Probably from scatterbrained)